U.S. patent application number 13/106849 was filed with the patent office on 2011-09-01 for superposition coding in a wireless communication system.
This patent application is currently assigned to QUALCOMM Incorporated. Invention is credited to Rashid Ahmed Akbar Attar, Naga Bhushan, Kiran Kiran.
Application Number | 20110211561 13/106849 |
Document ID | / |
Family ID | 38544005 |
Filed Date | 2011-09-01 |
United States Patent
Application |
20110211561 |
Kind Code |
A1 |
Kiran; Kiran ; et
al. |
September 1, 2011 |
SUPERPOSITION CODING IN A WIRELESS COMMUNICATION SYSTEM
Abstract
The present patent application comprises a method and apparatus
to compile a superposition coded packet by compiling user
candidates for superposition coding, ranking the user candidates
based on a result of an evaluation function, selecting a deserving
user candidate from among the user candidates, and compiling a
superposition coded packet by adding other user data packets to a
packet of the deserving user data packet, wherein the data packets
for the user candidates may conform to a plurality of different
formats and wireless communication standards.
Inventors: |
Kiran; Kiran; (Pleasanton,
CA) ; Bhushan; Naga; (San Diego, CA) ; Attar;
Rashid Ahmed Akbar; (San Diego, CA) |
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
38544005 |
Appl. No.: |
13/106849 |
Filed: |
May 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11567609 |
Dec 6, 2006 |
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13106849 |
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12860218 |
Aug 20, 2010 |
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11567609 |
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60794874 |
Apr 24, 2006 |
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Current U.S.
Class: |
370/335 |
Current CPC
Class: |
H04L 1/0006 20130101;
H04L 1/0025 20130101; H04L 1/18 20130101; H04L 5/04 20130101; H04L
1/0009 20130101; H04W 52/281 20130101; H04W 52/346 20130101; H04L
27/2602 20130101; H04L 1/0017 20130101; H04L 1/0003 20130101; H04L
5/023 20130101 |
Class at
Publication: |
370/335 |
International
Class: |
H04B 7/216 20060101
H04B007/216 |
Claims
1. A method comprising: compiling user candidates for superposition
coding; ranking the user candidates based on a result of an
evaluation function; selecting a deserving user candidate from
among the user candidates; determining whether to generate a
superposition coded packet based on a data rate requested by the
deserving user candidate; and adding other user data packets to a
packet of the deserving user candidate to generate the
superposition coded packet in response to determining to generate
the superposition coded frame, wherein the superposition coded
packet comprises a first packet formatted in accordance with a
first multiple access technique and at least one packet formatted
in accordance with a second multiple access technique.
2. The method of claim 1, wherein the evaluation function utilizes
at least one data rate request.
3. The method of claim 1, wherein the evaluation function
comprises: F i ( n ) = max i ( DRC i ( n ) R i ( n ) .times. 1 DRC
i ( n ) ) ##EQU00006## where, DRC.sub.i(n) represents the average
data rate requested by user "i" in a given time slot "n" over a
time window of appropriate size; R.sub.i(n) represents an average
data rate successfully received by user "i" over the time window of
the appropriate size; and max.sub.i( ) returns a maximum value for
determined parenthetical numeric values of user "i."
4. The method of claim 1, further comprising determining if there
are any pre-superposition coding criteria related to determining
whether to generate the superposition coded packet.
5. The method of claim 1, further comprising selecting the other
user data packets based on maximizing a throughput transmission
rate.
6. The method of claim 1, wherein the first multiple access
technique is based on a first wireless standard and wherein the
second multiple access technique is based on a second wireless
standard.
7. An apparatus, comprising: means for compiling user candidates
for superposition coding; means for ranking the user candidates
based on a result of an evaluation function; means for selecting a
deserving user candidate from among the user candidates; means for
determining whether to generate a superposition coded packet based
on a data rate requested by the deserving user candidate; and means
for adding other user data packets to a packet of the deserving
user candidate to generate the superposition coded packet in
response to determining to generate the superposition coded packet,
wherein the superposition coded packet comprises a first packet
formatted in accordance with a first multiple access technique and
at least one packet formatted in accordance with a second multiple
access technique.
8. The apparatus of claim 7, wherein the evaluation function
utilizes at least one data rate request.
9. The apparatus of claim 7, further comprising determining if
there are any pre-superposition coding criteria related to
determining whether to generate the superposition coded packet.
10. The apparatus of claim 7, further comprising means for
selecting the other user data packets based on maximizing a
throughput transmission rate.
11. The apparatus of claim 7, further comprising means for
eliminating, after selecting said deserving user candidate, from
the user candidates one or more user candidates having identical
requested data rates to the data rate requested by the deserving
user candidate.
12. A computer readable non-transitory tangible medium storing
instructions executable by a processor, the instructions
comprising: instructions that are executable by the processor to
compile user candidates for superposition coding; instructions that
are executable by the processor to rank the user candidates based
on a result of an evaluation function; instructions that are
executable by the processor to select a deserving user candidate
from among the user candidates; instructions that are executable by
the processor to determine whether to generate a superposition
coded packet based on a data rate requested by the deserving user
candidate; and instructions that are executable by the processor to
add other user data packets to a packet of the deserving user
candidate to generate the superposition coded packet in response to
determining to generate the superposition coded packet, wherein the
superposition coded packet comprises a first packet formatted in
accordance with a first multiple access technique and at least one
packet formatted in accordance with a second multiple access
technique.
13. The computer readable non-transitory tangible medium of claim
12, wherein the first multiple access technique is based on a first
wireless standard and wherein the second multiple access technique
is based on a second wireless standard.
14. The computer readable non-transitory tangible medium of claim
12, wherein the superposition coded packet further includes a third
packet formatted in accordance with a third multiple access
technique.
15. The computer readable non-transitory tangible medium of claim
12, further comprising instructions that are executable by the
processor to determine if there are any pre-superposition coding
criteria related to determining whether to generate the
superposition coded packet.
16. The computer readable non-transitory tangible medium of claim
12, further comprising instructions that are executable by the
processor to select the other user data packets based on maximizing
a throughput transmission rate.
17. An apparatus comprising: a processor configured to compile user
candidates for superposition coding, to rank the user candidates
based on a result of an evaluation function, to select a deserving
user candidate from among the user candidates, and to determine
whether to generate a superposition coded frame based on a data
rate requested by the deserving user candidate; and a summer to add
other user data packets to a packet of the deserving user candidate
to generate a superposition coded packet in response to determining
to generate the superposition coded frame, wherein the
superposition coded packet comprises a first packet formatted in
accordance with a first multiple access technique and at least one
packet formatted in accordance with a second multiple access
technique.
18. The apparatus of claim 17, wherein the first multiple access
technique is based on a first wireless standard and wherein the
second multiple access technique is based on a second wireless
standard.
19. The apparatus of claim 17, further comprising a multiplexer
configured to multiplex the superposition coded packet and a
preamble into a second superposition coded packet.
20. The apparatus of claim 17, wherein the at least one packet is
an orthogonal frequency-division multiple access (OFDMA) packet
modulated according to a plurality of frequencies allocated to a
plurality of user candidates other than the deserving user
candidate.
21. A method comprising: receiving a packet; reading a preamble;
determining from the preamble whether the packet is a superposition
coded packet; and processing the superposition coded packet at a
processor in response to determining that the packet is a
superposition coded packet, wherein the superposition coded packet
comprises a first packet formatted in accordance with a first
multiple access technique and at least one packet formatted in
accordance with a second multiple access technique.
22. The method of claim 21, wherein the first multiple access
technique is based on a first wireless standard and wherein the
second multiple access technique is based on a second wireless
standard.
23. The method of claim 21, further comprising determining if a
user is a most deserving user, wherein processing the superposition
coded packet comprises assuming that 100% of a total transmitted
power was allocated to the user if the user is the most deserving
user.
24. The method of claim 21, wherein the superposition coded packet
comprises at least one data packet for stronger users and at least
one data packet for weaker users and wherein processing the
superposition coded packet comprises: treating the at least one
data packet for the stronger users as interference and cancelling
the at least one data packet for the stronger users to generate
remaining packets; and decoding the remaining packets and
subtracting out the at least one data packet for weaker users from
the remaining packets.
25. The method of claim 24, wherein treating the at least one data
packet for the stronger users as interference and cancelling the at
least one data packet for the stronger users comprises using
successive interference cancellation.
26. The method of claim 21, further comprising sending an
acknowledgement related to the superposition coded packet.
27. An apparatus, comprising: means for receiving a packet; means
for reading a preamble; means for determining from the preamble
whether the received packet is a superposition coded packet,
wherein the superposition coded packet comprises a first packet
formatted in accordance with a first multiple access technique and
at least one packet formatted in accordance with a second multiple
access technique; and means for processing the superposition coded
packet in response to determining the packet is the superposition
coded packet.
28. The apparatus of claim 27, wherein the first multiple access
technique is based on a first wireless standard and wherein the
second multiple access technique is based on a second wireless
standard.
29. The apparatus of claim 28, wherein one of the first wireless
standard and the second wireless standard comprises an orthogonal
frequency-division multiplexing (OFDM) or an orthogonal
frequency-division multiple access (OFDMA) standard.
30. The apparatus of claim 27, further comprising means for
determining if a user is a most deserving user, wherein processing
the superposition coded packet comprises assuming that 100% of a
total transmitted power was allocated to the user if the user is
the most deserving user.
31. The apparatus of claim 27, wherein the superposition coded
packet comprises at least one data packet for stronger users and at
least one data packet for weaker users, and wherein processing the
superposition coded packet comprises: treating the at least one
data packet for stronger users as interference and cancelling such
data packets to generate remaining packets; and decoding the
remaining packets and subtracting out the at least one data packet
for weaker users from the remaining packets.
32. The apparatus of claim 31, wherein treating the at least one
data packet for stronger users as interference and cancelling such
data packets comprises using successive interference
cancellation.
33. A computer readable non-transitory tangible medium storing
instructions executable by a processor, the instructions
comprising: instructions that are executable by the processor to
receive a packet; instructions that are executable by the processor
to read a preamble; instructions that are executable by the
processor to determine from the preamble whether the packet is a
superposition coded packet; and instructions that are executable by
the processor to process the superposition coded packet at a
processor in response to determining that the packet is a
superposition coded packet, wherein the superposition coded packet
comprises a first packet formatted in accordance with a first
multiple access technique and at least one packet formatted in
accordance with a second multiple access technique.
34. The computer readable non-transitory tangible medium of claim
33, wherein the first multiple access technique is based on a first
wireless standard and wherein the second multiple access technique
is based on a second wireless standard.
35. The computer readable non-transitory tangible medium of claim
34, wherein one of the first wireless standard and the second
wireless standard comprises an orthogonal frequency-division
multiplexing (OFDM) or an orthogonal frequency-division multiple
access (OFDMA) standard.
36. The computer readable non-transitory tangible medium of claim
33, further comprising instructions that are executable by the
processor to determine if a user is a most deserving user, wherein
processing the superposition coded packet comprises assuming that
100% of a total transmitted power was allocated to the user if the
user is the most deserving user. instructions that are executable
by the processor to determine if a user is a most deserving user;
and
37. A mobile device comprising: a processor configured to receive a
packet, to read a preamble, to determine from the preamble whether
the packet is a superposition coded packet, and to process the
superposition coded packet in response to determining that the
packet is a superposition coded packet, wherein the superposition
coded packet comprises a first packet formatted in accordance with
a first multiple access technique and at least one packet formatted
in accordance with a second multiple access technique.
38. The mobile device of claim 37, wherein the first multiple
access technique is based on a first wireless standard and wherein
the second multiple access technique is based on a second wireless
standard.
39. The mobile device of claim 38, wherein one of the first
wireless standard and the second wireless standard comprises an
orthogonal frequency-division multiplexing (OFDM) or an orthogonal
frequency-division multiple access (OFDMA) standard.
40. The mobile device of claim 37, wherein the superposition coded
packet comprises at least one data packet for stronger users and at
least one data packet for weaker users, and wherein the processor
is configured to: treat the at least one data packet for stronger
users as interference and cancel such data packets to generate
remaining packets; and decode the remaining packets and subtract
out the at least one data packet for weaker users from the
remaining packets.
41. A method comprising: at a base station: compiling user
candidates for superposition coding; ranking the user candidates
based on a result of an evaluation function; selecting a deserving
user candidate from among the user candidates; determining whether
to generate a superposition coded frame based on the data rate
requested by the deserving user candidate; adding other user data
packets to a packet of the deserving user candidate to generate a
superposition coded packet in response to determining to generate
the superposition coded frame; and transmitting the superposition
coded packet to multiple users including the deserving user
candidate, wherein the superposition coded packet comprises a first
packet formatted in accordance with a first multiple access
technique and at least one packet formatted in accordance with a
second multiple access technique.
42. The method of claim 41, wherein the first multiple access
technique is based on a first wireless standard and wherein the
second multiple access technique is based on a second wireless
standard.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119 AND 35 U.S.C.
.sctn.120
[0001] The present Application for Patent is a Divisional and
claims priority to patent application Ser. No. 11/567,609 filed
Dec. 6, 2006, pending, which claims priority to Provisional
Application No. 60/794,874 filed Apr. 24, 2006, and assigned to the
assignee hereof and hereby expressly incorporated by reference
herein.
REFERENCE TO CO-PENDING APPLICATION FOR PATENT
[0002] This Application is co-pending with Divisional patent
application Ser. No. 12/860,218 filed Aug. 20, 2010, and assigned
to the assignee hereof and hereby expressly incorporated by
reference herein.
BACKGROUND
[0003] 1. Field of the Invention
[0004] The present invention relates generally to methods and
apparatus to schedule and wirelessly transmit information packets
and more specifically to employ superposition coding to improve the
forward link (FL) data throughput performance in a wireless
communication system.
[0005] 2. Background
[0006] There are a variety of wireless communication standards that
may control the communication in a cellular communication system.
The cdma2000 1xEV-DO standard ("cdma2000 High Rate Packet Data Air
Interface Specification," TIA/EIA/IS-856) is a system for packet
data communication developed by Qualcomm Inc., U.S.A. in the late
1990's to provide general data communication services in a wireless
mobile environment. The 1xEV-DO system adopts intrinsic resource
assignment methods corresponding to the characteristics of forward
and reverse links.
[0007] Under the 1xEV-DO standard, the base station may transmit
one data packet to one cell phone during that moment in time. In
operation, a base station may continuously transmit pilot signals
with a constant power. On receiving a pilot signal, a cell phone
determines the intensity of the received pilot signal and sends the
results back to the base station in the form of a requested Data
Rate Control (DRC).
[0008] Fading is the probabilistic variation in the received
intensity of a radio transmission. The phone's distance from the
base station may affect the received pilot signal intensity. Also,
dynamic events, such a truck passing between the cell phone and
base station, the pilot signal reflecting off buildings to combine
with or cancel the main pilot signal, may affect the received pilot
signal intensity. In short, distance and interference conditions
create disparity in this Forward Link
Signal-to-Interference-and-Noise Ratio (FL SINR) and thus affect
the requested DRC of each phone.
[0009] At the base station, a scheduler method may rank each cell
phone by its pilot signal intensity (namely, requested DRC) and
utilize that ranking to determine which one cell phone may receive
the next data packet. In a typical intrinsic resource assignment
method, the base station may send out that data packet which
corresponds to the cell phone having the "most" deserving
signal-to-interference-to-noise ratio (SINR). Which cell phone is
most deserving may be decided by a scheduling method which may rank
each cell phone based on a result of an evaluation function. During
that moment in time, the most deserving user's needs may be
addressed while the needs of the remaining users (in the above
example, the needs of twenty-nine users) may have to wait.
[0010] Conventional intrinsic resource assignment methods attempt
to provide fair service to all cell phones. This leads to a problem
in that the weakest set of users limit the overall system data
throughput performance Moreover, users with lower FL SINRs are
penalized with a lower than potential throughput and higher delays
for their particular cell phone. There is therefore a need in the
art for a system that improves the forward link data throughput
performance and diminishes the delays for users with FL SINRs that
are lower than the FL SINR of the stronger set of users while
meeting the needs of the most deserving (possibly weaker set of)
users).
SUMMARY
[0011] Embodiments disclosed herein address the above stated needs
by using superposition coding for multiple candidates, one of which
is the "most" deserving user, by selecting a 2-user, 3-user, or
N-user combination that maximizes the forward link data throughput
performance of the wireless communication system, and by
dynamically reallocating the power transmission at the start of
each time slot interlace.
[0012] A system to communicate a superposition coded packet from a
base station to a plurality of remote stations is disclosed. At the
base station, a list of user candidates for superposition coding
may be compiled and the most deserving user among the user
candidates may be determined. One embodiment limits superposition
coding to no more than four user candidates, however, other
embodiments may code with a different number of users. Those user
candidates who have a requested data rate that may be less than a
requested data rate of the most deserving user may be eliminated. A
superposition coded packet may be compiled from the remaining user
candidates. The various users in the superposition coded packet may
use different modulation techniques and/or packet formats. For
example, the lowest layer may use packet formats of a 1xEV-DO
Revision A system.
[0013] The other users might use packet formats that utilize
Orthogonal Frequency Domain Modulation (OFDM). Others may also use
OFDMA (with different power allocation across the
sub-carriers).
[0014] If a remote mobile receiving the superposition coded packet
is the lowest layer, then that remote station may process the
superposition coded packet by assuming alternatively that some
apriori known fraction of power allocated to the lowest layer as
well as all power allocated to the lowest layer. Further, if one or
more users are successful in decoding before the nominal length of
the data packet, their power may be re-allocated to another
user.
[0015] The embodiments may be applied to a variety of applications.
For example, when applied to a Voice-over-Internet Protocol (VoIP),
the inventive superposition coding may allow for lower latencies
(reduced transmission delays), a greater number of users per sector
(namely, a higher capacity), or a combination of the two. When
applied to broadcast services such as advertising, the broadcast
services may be superposition coded with unicast traffic directed
to an individual user so that both broadcast and unicast traffic
may be transmitted together. This broadcast service may be the
common information intended for all users (like the control channel
in 1xEV-DO) or information intended for a particular region (like
the information transmitted using platinum broadcast, also known as
"cdma2000.RTM. High Rate Broadcast-Multicast Packet Data Air
Interface Specification," TIA-1006-A). Thus, unlike conventional
wireless communication systems, the present invention minimizes or
eliminates the need to preempt broadcast traffic with unicast
traffic. In other words, broadcast traffic need not be compromised
during periods of unicast traffic for those systems employing the
present method and apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an illustration of a typical OFDM signal within an
OFDM channel bandwidth showing the frequency domain positioning of
OFDM sub-carriers according to the art;
[0017] FIG. 2 shows three tones over a single symbol period, where
each tone has an integer number of cycles during the symbol;
[0018] FIG. 3 is a block diagram of the basic operations of a GSM
cellular system;
[0019] FIG. 4 illustrates a GSM burst structure;
[0020] FIG. 5 is a perspective view of a wireless communication
system;
[0021] FIG. 6 is a detailed plan view of a cell of FIG. 5;
[0022] FIG. 7 is flowchart comprising the steps of method 300 used
to compile fixed length information packets into a superposition
coded packet having an address header;
[0023] FIG. 8A is a table listing each user, an example DRC for
each user, and an example resulting evaluation function F(n) for
each user;
[0024] FIG. 8B is a table listing of the contents of FIG. 6A as
sorted by the DRC for each user;
[0025] FIG. 8C is a table listing of the contents of FIG. 6A as
sorted by the resulting evaluation function F(n) for each user;
[0026] FIG. 9A is a logic block diagram for the apparatuses used to
compile, transmit, and process a superposition coded packet;
[0027] FIG. 9B is an example of a logic block diagram for the
apparatuses used to compile, and transmit a superposition coded
packet, where the various users improve spectral efficiency by
utilizing different modulation methods;
[0028] FIG. 9C shows how the various packets are fit in
time-domain, with each user receiving a fraction of the power;
[0029] FIG. 9D illustrates a 1xEV-DO forward link slot format used
in one embodiment of the present method and apparatus;
[0030] FIG. 9E illustrates a mixed data slot using different packet
formats;
[0031] FIG. 9F illustrates a 1xEV-DO forward link slot format used
in the current embodiment, with layer 2 using OFDMA type packet
format;
[0032] FIG. 9G illustrates a mixed data slot where one layer uses a
GSM packet format;
[0033] FIG. 10 is a flowchart containing the steps of method 600
which compiles, transmits, and processes one or more data
packets;
[0034] FIG. 11 is an example of two layer OFDMA superposition
coding packet with a nominal span equal to two slots;
[0035] FIG. 12 is a computer system 700 with which some embodiments
of the present method and apparatus may be implemented;
[0036] FIG. 13 is block diagram comprising means plus function
blocks used to compile fixed length information packets into a
superposition coded packet having an address header; and
[0037] FIG. 14 is a block diagram comprising means plus function
blocks used to compile, transmit, and process one or more data
packets.
DETAILED DESCRIPTION
[0038] Millions of people in the United States and around the world
utilize cellular phones. One of the most interesting things about a
cell phone is that it is actually a sophisticated radio. To provide
communication, these sophisticated radios may be incorporated into
a radiotelephone system such as a cellular system.
[0039] In a cellular system, a geographic area such as a city may
be divided into a number of cells. Each cell may have a base
station that includes a tower and a small building containing radio
equipment. The base station within a cell may service the
communication link needs of the cell phones located within that
cell.
[0040] The communication link needs of a cell phone may be broken
into two areas: reverse link (cell phone to base station link) and
forward link (base station to cell phone link). During forward link
operations, a base station may transmit data packets to the cell
phones located within that cell. For example, at any one moment in
time (e.g., during 1.67 milliseconds), the base station may have
thirty different cell phone users requesting data.
[0041] There are a variety of wireless communication standards that
may control the communication in a cellular communication system.
The cdma2000 1xEV-DO standard ("cdma2000 High Rate Packet Data Air
Interface Specification," TIA/EIA/IS-856) is a system for packet
data communication developed by Qualcomm Inc., U.S.A. in the late
1990's to provide general data communication services in a wireless
mobile environment. The 1xEV-DO system adopts intrinsic resource
assignment methods corresponding to the characteristics of forward
and reverse links.
[0042] The wireless communication standard may have different
modulation techniques (for example, Code Division Multiple Access
(CDMA), Orthogonal Frequency Division Multiplexing (OFDM),
Orthogonal Frequency Division Multiple Access (OFDMA), etc.) in
order to improve spectral efficiency. In one or more embodiments,
the features of the present patent application may be used with
these various forms of modulations. For example, although not
limited to, it may be used with the OFDM disclosed in CDMA2000
1xEV-DO Rev C.
[0043] OFDM is a multi-carrier transmission technique, which
divides the available spectrum into many equally spaced carriers or
tones and carries a portion of a user's information on each tone.
OFDM can be viewed as a form of frequency division multiplexing
(FDM), however, OFDM has an important special property that each
tone is orthogonal with every other tone. High-speed data signals
are divided into tens or hundreds of lower speed signals. An OFDM
system takes a data stream and splits it into N parallel data
streams, each at a rate 1/N of the original rate. These lower speed
signals are transmitted in parallel over respective frequencies
within a radio frequency (RF) signal that are known as sub-carrier
frequencies ("sub-carriers") or tones. A sub-carrier or tone is
modulated by one of the low rate data streams, thereby producing a
data tone. In addition, a sub-carrier may be modulated by a pilot
signal, thereby producing a pilot tone. Thus, the OFDM signal is a
sum of many signals with different subcarrier frequencies.
[0044] In addition, all of the carriers are orthogonal to one
another. Because the carriers are orthogonal, each carrier has an
integer number of cycles over a symbol period. Due to this, the
spectrum of each carrier has a null at the center frequency of each
of the other carriers in the system. See FIG. 1. Thus, the peak of
each tone corresponds to a zero level, or null, of every tone. As a
result, there is minimal interference between the carriers,
allowing then to be spaced as close as theoretically possible. When
the receiver samples at the center frequency of each tone, the only
energy present is that of the desired signal, plus whatever other
noise happens to be in the channel.
[0045] FIG. 2 shows three data tones over a single symbol period,
where each tone has an integer number of cycles during the
symbol.
[0046] The OFDM signal will retain its sub-carrier orthogonality
property when transmitted through a non-dispersive channel.
However, most channels are dispersive. Thus, significant time
and/or frequency dispersion are introduced into the transmitted
signal. These impairments introduce inter-carrier interference
(ICI) and inter-symbol interference (ISI) and which can destroy the
orthogonality of the sub-carriers.
[0047] To protect against time dispersions including multi-path, a
guard interval equal to the length of the channel impulse response
is introduced between successive OFDM symbols. The cyclic extended
OFDM symbol thus consists of a guard interval and a useful part in
which information is transmitted. The guard interval is commonly
implemented by cyclic extension of the inverse fast Fourier
transform (IFFT) output (i.e., cyclic retransmission of part of the
periodic transform). To maintain transmission efficiency, system
designers typically endeavor to limit the guard interval to less
than one quarter of the useful OFDM symbol duration.
[0048] OFDM can also be considered a multiple access technique
since individual tones or groups of tones can be assigned to
different users. Each user may be assigned a predetermined number
of tones when they have information to send, or alternatively, a
user may be assigned a variable number of tones based on the amount
of information they have to send. The assignments are controlled by
the media access control layer (MAC) layer, which schedules the
resource assignments based on user demand. In OFDMA, there is an
added feature that the power assigned to different tones (users)
can also be different (as shown in FIG. 9F), while satisfying the
average power constraints over the entire bandwidth.
[0049] The global system for mobile communications (GSM) is a
digital cellular communications standard which was initially
developed in Europe and has gained rapid acceptance and market
share worldwide. It was originally designed to be compatible with
the integrated services digital network (ISDN) standard. Thus, the
services provided by GSM are a subset of the standard ISDN
services, speech being the most basic. A broader range of criteria
in the development of GSM include spectrum efficiency,
international roaming, low cost mobile and base stations, voice
quality and the ability to support new services. Over time, the GSM
standard has broadened and evolved to include a variety of channel
and coding formats.
[0050] FIG. 3 is a block diagram of the basic operations of a GSM
cellular system 9100. The system 9100 can be viewed as a series of
processes which are performed on an audio source (e.g., speech) to
take it from a source and reasonably reproduce it at a receiver.
The source processes 9102, represented by the top row of
operations, can be performed by a mobile station (e.g., a cell
phone). The receiving processes 9104, represented by the bottom row
of operations, can be performed at the base station. In general,
the receiving processes 9104 are the reverse of the source
processes 9102, performed in reverse order.
[0051] The GSM standard generally uses two frequency bands, each
having a bandwidth of 25 MHz. The GSM-900 system operates at
frequencies in two bands around 900 MHz (mega-hertz). One band,
comprising the 890-915 MHz range, is allocated for uplink
transmissions, transmitting from the mobile station to the base
station. Another band, comprising the 935-960 MHz range, is
allocated for downlink transmissions, transmitting from the base
station to the mobile station. The GSM-1800 system (also called
DCS) operates in two bands around 1800 MHz. The GSM-1900 system
(also called PCS) operates in two bands around 1900 MHz.
[0052] Depending upon frequency allocation within particularly
countries, regional variations of the actually frequency bands can
occur.
[0053] The GSM standard employs a multiple access scheme that
defines how simultaneous communication can occur between different
mobile stations and base stations. A geographic cell structure of
base stations provides a spatial diversity for the defined
frequency spectrum. Within each cell, a combination of frequency
division multiple access (FDMA) and time division multiple access
(TDMA) techniques are employed by the standard. Each 25 MHz band is
divided into 124 carrier frequencies spaced at 200 kHz intervals
applying FDMA. Each of the carrier frequencies is then time wise
divided into eight bursts, each lasting approximately 0.577 ms
applying TDMA. The eight bursts for each carrier are viewed as a
single "frame", lasting approximately 4.615 ms; a single user will
employ one of the bursts within the frame. In this manner
individual "channels" are formed which each correspond to a
particular carrier frequency and burst number. Referring back to
FIG. 3, the communication process for a particular mobile to base
station communication link according to the GSM standard can now be
described.
[0054] Speech coding 9106 at the first mobile base station converts
incoming analog speech to a digital signal. Channel coding 9108
adds extra bits to the original information in order to aid in
detecting and possibly correcting any errors occurring during the
signal transmission.
[0055] The interleaving 9110 operation rearranges a group of bits
in a particular way. The effect of interleaving is to reduce the
likelihood of errors in the data stream. In general, because errors
are more likely to affect consecutive bits within a burst,
interleaving disperses the bits across bursts.
[0056] Following interleaving 9110, the burst assembling 9112
procedure groups the bits into bursts for transmission. FIG. 4
illustrates a normal burst structure 9200. The normal burst
structure 9200 comprises a multi-frame including 26 individual
frames (numbered 0 through 25). Traffic channels 9202 occupy frames
0 through 11 and 13 through 24. Frame 12 is used for the slow
associated control channel (SACCH) 9204. Frame 25 is unused in the
case of a single full rate traffic channel, but employed as a
second SACCH 9206 in the case of two half rate traffic channels.
Furthermore, in the case of two half rate channels, the even
numbered frames (except frame 12) are used as traffic for a first
user and the odd numbered frames (except frame 25) are used as
traffic for a second user. Each frame of the traffic channels 9202
comprises 8 bursts 9208 (numbered 0 through 7) and each burst 9208
has a structure as follows. The tail bits groups 9210, 9222 each
comprise three bits set to zero and disposed at the beginning and
the end of a burst 9208. They are used to cover the periods of
ramping up and down of the mobile's power. Coded data groups 9212,
9220 each comprise 57 bits, containing signaling or user data.
Stealing flags 9214, 9218 are used to indicate to the receiver
whether the information carried by a burst 9208 corresponds to
traffic or signaling data. The training sequence 9216 has a length
of 26 bits. It is used to synchronize the receiver with the
incoming information, avoiding then the negative effects produced
by a multipath propagation. The guard period 9224, with a length of
8.25 bits, is used to avoid a possible overlap of two mobiles
during the ramping time.
[0057] Referring back to FIG. 3, ciphering 9114 is used to protect
signaling and user data. After ciphering 9114, the transmitted
signal 9118 is formed by modulation 9116. Typically, the GSM
standard employs a Gaussian Minimum Shift Keying (GMSK) modulation.
The GMSK modulation has been selected as a compromise between
spectrum efficiency, complexity and low spurious radiation
(reducing the possibilities of adjacent channel interference). The
GMSK modulation has a rate of 270 kbauds and a BT product equal to
0.3. Alternately, the GSM standard can also utilize an 8 phase
shift keying (8-PSK) modulation for enhanced data for GSM evolution
(EDGE) applications.
[0058] The modulated signal 9118 is then transmitted to a receiver,
e.g. a base station, where the receiving operations 9104 are
performed. The receiving processes include (in order) demodulating
9120, deciphering 9122, burst disassembly 9124, deinterleaving
9126, channel decoding 9128 and speech decoding 9130. These
operations are the inverse of their respective transmission
operations discussed above.
[0059] FIG. 5 is a perspective view of a wireless communication
system 100. Wireless communication system 100 may be a collection
of individual communications networks, transmission systems, relay
stations, tributary stations, and/or data terminal equipment
capable of interconnection and interoperation to form an integrated
whole. Wireless communication system 100 may include a geographic
area 102 divided into a grid 104 containing a number of cells 106,
here cells 108, 110, 112, 114, 116, 118, 120, 122, and 124. For
example, a city or county may be divided into smaller cells. Cells
106 may vary in size depending upon terrain, capacity demands, and
other factors. For example, in one embodiment each cell 106 has a
hexagonal shape and is sized to about 10 square miles (26 square
kilometers).
[0060] Wireless communication system 100 further may include a
number of base stations 126, for example base stations 128, 130,
132, 134, 136, 138, 140, 142, and 144. Each cell 106 may have a
base station 126. Base station 126 may be a radio transceiver
(transmitter/receiver) that uses processing hardware/software,
transmission power, and an antenna array to control and relay voice
and data signals between two devices. Base station 126 may be a
High Data Rate (HDR) base station apparatus and may be referred to
as a Modem Pool Transceiver (MPT). By controlling the transmission
power from each base station 126, radio frequencies assigned to
each cell 106 may be limited to the boundaries of that particular
cell 106. In this way, the same frequencies may be assigned to cell
108 and cell 118, for example.
[0061] FIG. 6 is a detailed plan view of cell 110 of FIG. 5.
Included within cell 110 may be Access Terminals (ATs), such as ATs
202, 204, 206 . . . 240. An AT 202-240 may be any data device that
communicates through a wireless channel 201, 203, 205 or through a
wired channel, for example using fiber optic or coaxial cables.
Moreover, an AT 202-240 may further be any of a number of types of
devices including but not limited to PC card, compact flash,
external modem, internal modem, wireless phone, or wireline
phone.
[0062] Each AT 202-240 may be referred to as a user and may include
a cell phone, a mobile station, a base mobile transceiver, a
satellite, a mobile radiotelephone set, a base mobile transceiver,
a remote station apparatus, or a High Data Rate (HDR) subscriber
station. Moreover, each AT 202-240 may be mobile or stationary and
may be adapted to communicate data packets with one or more base
stations 126-142 (FIG. 5) through reverse links 201. AT 202 may
transmit and receive data packets through one or more base stations
126-142 to an HDR base station controller, which may be referred to
as a Modem Pool Controller (MPC).
[0063] Modem pool transceivers and modem pool controllers may be
parts of a network called an Access Network (AN). An AT 202-240 may
be that portion of a public or private switched network that
connects access nodes to individual subscribers. For example, an AN
may transport data packets between multiple ATs 202-240. The AN may
further connect to additional networks outside the AN, such as a
corporate intranet or the Internet, and may transport data packets
between each AT 202-240 and such outside networks. Collectively or
in portions thereof, these may be parts of wireless communication
system 100.
[0064] An AT 202-240 having established an active traffic channel
connection with one or more base stations 126 may be referred to as
an active AT 202-240. An active AT 202-240 is said to be in a
traffic state. An AT 202-240 that is in the process of establishing
an active traffic channel connection with one or more base stations
126-144 is said to be in a connection setup state.
[0065] Reverse links 201 (FIG. 6) may be radio interfaces that
connects the AT 202-240, such as AT 214, to AN services provided by
base station 130. For example, AT 202 may be adapted to communicate
data packets with base station 130 through a reverse link 203 and
AT 204 may be adapted to communicate data packets with base station
130 through a reverse link 205 (see FIG. 5).
[0066] A data packet may be viewed as a block of data arranged in
the form of a packet having a preamble and a payload. The preamble
may carry overhead information about the content of the packet and
destination address; and the payload may then be the user
information. Typically, a base station 126-142 transmits a data
packet to one user 202-240 at a time (single user packet) or to
multiple users at a time (multi-user data packet). The data portion
in the payload can be formed utilizing different modulation
techniques, to improve spectral efficiency. In the example
flowchart shown in FIG. 7, the most deserving user 202 utilizes the
packet format prescribed by the 1xEV-DO Rev B system, while the
other users 204, 218, 232 use the OFDM packet formats. The proposed
method of superposition coding applies to a system where each layer
may have a payload constructed using different multiple access
techniques.
[0067] Superposition coding is a technique where two or more data
packets may be combined at the base station 126-142 as a
superposition coded packet and transmitted with scaled power to
multiple users at a moment in time. As in T. M. Cover, Broadcast
Channels, IEEE Transactions on Information Theory, IT-18 (1): Feb.
14, 1972, signals to different users are superposed on each other
and transmitted with different powers in the same data packet. An
aspect of the present method and apparatus employs superposition
coding to improve the data throughput capacity from a base station
126-142, such as base station 130 (FIG. 6), to ATs 202-240 in a
wireless communication system 100. The superposition coded packets
shared a common resource, namely "power;" while the multi-user
packets share a common resource, namely "time."
[0068] The combining of two data packets may be achieved with
superposition by (1) scaling the first set of symbol substreams
with a first scaling factor, (2) scaling the second set of symbol
substreams with a second scaling factor, and (3) summing the first
set of scaled symbol substreams with the second set of scaled
symbol substreams to obtain the multiple transmit symbol streams.
The first and second scaling factors determine the amount of
transmit power to use for the base stream and enhancement stream,
respectively.
[0069] FIG. 7 is a flowchart containing the steps of a method 300
used to compile fixed length information packets into a
superposition coded packet having an address header. In radio
communications, a forward link traffic channel 504 (e.g., forward
link) is typically the link from a fixed location (e.g., a base
station) to a mobile user 202. If the link 504 includes a
communications relay satellite, the forward link 504 may consist of
both an uplink (base station to satellite) and a downlink
(satellite to mobile user).
[0070] The forward link channel 504a-d of method 300 may be of a
single data channel that is divided into plural time slots. For
reference only, the length of each time slot may be 1.67
milliseconds (msec). As noted above, a base station 126 typically
transmits one data packet during a single time slot. For a forward
link channel 504 with "i" number of users, method 300 considers the
transmission of one or more data packets during a single time slot
"n." As will be shown, by transmitting more than one data packet
during a single time slot, the method 300 works to improve the data
throughput rate on the forward link channel 504 towards the
theoretical peak data throughput rate on the forward link channel
504. It should be noted that the packet formats of different users
may conform to different wireless communication standards.
[0071] A pilot signal may be viewed as a signal transmitted over a
communications system for supervisory, control, equalization,
continuity, synchronization, or reference. In method 300,
transmitted pilot signals may be used to support channel estimation
for coherent detection. At step 302, base station 130 may
continuously transmit pilot signals with a constant power. Each AT
202 may then receive a pilot signal.
[0072] During its travel from base station 130 to an AT 202-240,
the intensity or strength of the pilot signal may vary due to the
distance from the base station 130, interference from other base
stations 126, 128, 132-142, shadowing, short-term fading, and
multi-path. Thus, each AT 202-240 may predict an achievable
Signal-to-Interference-and-Noise Ratio (SINR) from its received
pilot signal. From the predicted SINR, each AT 202-240 may compute
a DRC. The data rate control (sometimes referred to as requested
data rate) may represent the information transmission rate that the
AT 202-240 may support in the near future while maintaining a given
Packet Error Rate (PER), such as a 1% PER. In other words, the
requested DRC may be the best rate at which an AT 202-240 predicts
that it may be reliably served by base station 130 for a given time
slot.
[0073] At step 308, base station 130 may receive a requested DRC
from each AT 202-240. Each received DRC may represent a request for
immediate service by an AT 202-240. A present problem with typical
wireless communications is that not all ATs 202-240 requesting
immediate service may be served at the same time. Thus, base
station 130 may select those ATs 202-240 whose needs may be served
for a give time slot through resource allocation decisions.
[0074] Resource allocation decisions may be concerned with the
allocation of limited resources to achieve the best system
performances. In method 300 at step 310, base station 130 may
employ a scheduler 714 to engage a ranking metric, such as a
scheduler method, to rank each AT 202-240 based on a result of an
evaluation function that utilizes the requested DRC of each AT
202-240. The ranking may be used to determine which data packet(s)
may be transmitted during the single time slot "n," preferably to
maximize individual data throughput and system data throughput
while maintaining some notion of fairness.
[0075] Examples of scheduling algorithms include Round Robin (RR),
Weighted Round Robin (WRR), Bandwidth On Demand (BOD), Equal Grade
of Service (E-GoS), Proportionally Fair (PFair) and those utilizing
delay parameters. Preferably, method 300 employs a scheduling
algorithm that attempts to provide a fair (equal) treatment of all
the competing ATs 202-240 while efficiently allocating resources.
For example, method 300 may employ the Proportionally fair (P-fair)
fairness metric or the Equal Grade of Service (E-GoS) fairness
metric at step 310.
[0076] Under the P-fair metric, the scheduler 714 may take
advantage of the short-term time variations of the forward link
channel 504 by scheduling transmissions to ATs 202-240 during
periods where the ATs 202-240 see strong signal levels. Here, the
scheduler 714 may employ the method:
F i ( n ) = max i ( DRC i ( n ) R i ( n ) ) ( 1 ) ##EQU00001##
[0077] where, [0078] F.sub.i(n) is the evaluation function for user
"i" at time slot "n," where i=1, . . . , N; [0079] DRC.sub.i(n) is
the instantaneous data rate requested by user "i" in the time slot
"n"; [0080] R.sub.i(n) is the average data rate successfully
received by user "i" over a time window of appropriate size; and
[0081] max.sub.i(.cndot.) returns the maximum value for the
determined parenthetical numeric values of user "i."
[0082] Using the P-fair metric of equation (1), each user "i" may
be served in time slots in which its requested rate is closer to
the peak compared to its recent requests. By way of comparison, a
scheduler 714 employing an E-GoS metric additionally takes into
account the average data rate at which user "i" has requested to be
served over a time window of appropriate size. Here, each user "i"
may be provided an approximately equal opportunity to receive a
data packet without regard to channel condition so as not to
penalize a user 202-240 for moving within the system. In other
words, each user "i" may be given enough time for all ATs 202-240
to achieve the same average data rate over a time window of
appropriate size. As an E-GoS metric, the scheduler 714 may
employ:
F i ( n ) = max i ( DRC i ( n ) R i ( n ) .times. 1 DRC i ( n ) ) (
2 ) ##EQU00002##
[0083] where,
[0084] DRC.sub.i(n) represents the average data rate requested by
user "i" in the given time slot "n" over a time window of
appropriate size. As may be determined from equation (2), as the
average data rate requested by user "i" decreases, the evaluation
function F.sub.i(n) for user "i" increases, making it more likely
that user "i" may be served in the given time slot "n".
[0085] At step 312, base station 130 may determine which single
user "i" is to be served in the given time slot "n." This decision
epoch may be achieved by selecting that user "i" with greatest
value for the evaluation function F.sub.i(n). A user 202-240 having
the greatest value for the evaluation function F.sub.i(n) may
reflect that such a user 202-240 is the most deserving (e.g.
weakest, but recovering) user 202-240. It may be helpful at this
point to provide a numerical example.
[0086] FIG. 8A is a table listing each user 202 through 240, an
example DRC for each user 202-240, and an example resulting
evaluation function F(n) for each user 202-240. Each DRC may be
measured in kilobits per second (kbps). FIG. 8B is a table listing
of the contents of FIG. 8A as sorted by the DRC for each user
202-240. FIG. 8C is a table listing of the contents of FIG. 8A as
sorted the resulting evaluation function F(n) for each user
202-240. If the results of FIG. 8C were used by base station 130,
user 202 would have the greatest value for the evaluation function
F.sub.i(n), namely F.sub.i(n)=45. Thus, base station 130 may
determine that user 202 is the most deserving user 202 and
determine at step 312 that user 202 is to be served in the given
time slot "n."
[0087] With the single user "i" is to be served in the given time
slot "n" selected at step 312, there may be certain criteria that
should be met before determining whether to bundle the data packet
of the most deserving user 202 with other data packets into a
superposition coded packet. Thus, method 300 may determine at 314
whether there are any pre-superposition coding criteria and, if
there are, method 300 may determine at 316 whether all
pre-superposition coding criteria have been met. Pre-superposition
coding criteria may be a function of the particular standard
employed by a wireless communication system. One wireless
communication standard is the cdma2000 1xEV-DO standard ("cdma2000
High Rate Packet Data Air Interface Specification,"
TIA/EIA/IS-856).
[0088] The cdma2000 1xEV-DO standard is a system for packet data
communication to provide general data communication services in a
wireless mobile environment. The 1xEV-DO system adopts intrinsic
resource assignment methods corresponding to the characteristics of
forward 504 and reverse links 201.
[0089] The forward traffic channel is a packet-based, variable-rate
channel. The user physical layer packets for an access terminal may
be transmitted as shown in Table 1A at a data rate that varies from
4.8 kbps to 3.072 Mbps. Table 1A below lists the modulation
parameters for the physical layer packets for the forward traffic
channel and the control channel of the 1xEV-DO rev B forward link
504.
TABLE-US-00001 TABLE 1A Transmission Format (Physical Layer Packet
Size(bits), Nominal Nominal Transmit Duration (slots), Modulation
Data Rate Preamble Length (chips)) Code Rate Type (kbps) (128, 16,
1024) 1/5 QPSK 4.8 (128, 8, 512) 1/5 QPSK 9.6 128, 4, 1024) 1/5
QPSK 19.2 (128, 4, 256) 1/5 QPSK 19.2 (128, 2, 128) 1/5 QPSK 38.4
(128, 1, 64) 1/5 QPSK 76.8 (256, 16, 1024) 1/5 QPSK 9.6 (256, 8,
512) 1/5 QPSK 19.2 (256, 4, 1024) 1/5 QPSK 38.4 (256, 4, 256) 1/5
QPSK 38.4 (256, 2, 128) 1/5 QPSK 76.8 (256, 1, 64) 1/5 QPSK 153.6
(512, 16, 1024) 1/5 QPSK 19.2 (512, 8, 512) 1/5 QPSK 38.4 (512, 4,
1024) 1/5 QPSK 76.8 (512, 4, 256) 1/5 QPSK 76.8 (512, 4, 128) 1/5
QPSK 76.8 (512, 2, 128) 1/5 QPSK 153.6 (512, 2, 64) 1/5 QPSK 153.6
(512, 1, 64) 1/5 QPSK 307.2 (1024, 16, 1024) 1/5 QPSK 38.4 (1024,
8, 512) 1/5 QPSK 76.8 (1024, 4, 256) 1/5 QPSK 153.6 (1024, 4, 128)
1/5 QPSK 153.6 (1024, 2, 128) 1/5 QPSK 307.2 (1024, 2, 64) 1/5 QPSK
307.2 (1024, 1, 64) 1/3 QPSK 614.4 (2048, 4, 128) 1/3 QPSK 307.2
(2048, 2, 64) 1/3 QPSK 614.4 (2048, 1, 64) 1/3 QPSK 1,228.8 (3072,
2, 64) 1/3 QPSK 921.6 (3072, 1, 64) 1/3 QPSK 1,843.2 (4096, 2, 64)
1/3 QPSK 1,228.8 ((4096, 1, 64) 1/3 QPSK 2,457.6 (5120, 2, 64) 1/3
QPSK 1,536.0 (5120, 1, 64) 1/3 QPSK 3,072.0
[0090] Table 1B below lists the modulation parameters for the
optional user physical layer packets on the forward traffic channel
and the control channel of the 1xEV-DO rev B forward link 504. If
transmitted, they may be transmitted at a data rate that varies
from 153.6 kbps to 4.915 Mbps.
TABLE-US-00002 TABLE 1B Transmission Format (Physical Layer Packet
Size(bits), Nominal Nominal Transmit Duration (slots), Modulation
Data Rate Preamble Length (chips)) Code Rate Type (kbps) (1024, 4,
64) 1/5 QPSK 153.6 (2048, 4, 64) 1/3 QPSK 307.2 3072, 4, 64) 1/3
QPSK 460.8 (4096, 4, 64) 1/3 QPSK 614.4 (5120, 4, 64) 1/3 8-PSK
768.0 (6144, 4, 64) 1/3 16-QAM 921.6 (6144, 2, 64) 1/3 64-QAM
1,843.2 (6144, 1, 64) 1/3 64-QAM 3,686.4 (7168, 4, 64) 1/3 16-QAM
1,075.2 (7168, 2, 64) 1/3 64-QAM 2,150.4 (7168, 1, 64) 1/3 64-QAM
4300.8 (8192, 4, 64) 1/3 16-QAM 1,228.8 (8192, 2, 64) 1/3 16-QAM
2,457.6 (8192, 1, 64) 1/3 64-QAM 4,915.2
[0091] DRC indexes in 1xEV-DO Rev B have a set of associated
transmission formats for single-user packet and multi-user packet.
A detailed listing of DRC indices and their associated transmission
formats is provided in Table 1C.
TABLE-US-00003 TABLE 1C Transmission RevB RevB Formats Termination
Maximum Single User Multi-User for 1xEV-DO Rate Target Span
Transmission Transmission RevB DRC Index kbps (slots) (slots)
Formats Formats 0x00 0 16 16 (128, 16, 1024), (128, 4, 256), (256,
16, 1024), (256, 4, 256), (512, 16, 1024), (512, 4, 256), (1024,
16, 1024) (1024, 4, 256) 0x01 38.4 16 16 (128, 16, 1024), (128, 4,
256), (256, 16, 1024), (256, 4, 256), (512, 16, 1024), (512, 4,
256), (1024, 16, 1024) (1024, 4, 256) 0x02 76.8 8 8 (128, 8, 512),
(128, 4, 256), (256, 8, 512), (256, 4, 256), (512, 8, 512), (512,
4, 256), (1024, 8, 512) (1024, 4, 256) 0x03 153.6 4 8 (128, 4,
256), (128, 4, 256), (256, 4, 256), (256, 4, 256), (512, 4, 256),
(512, 4, 256), (1024, 4, 256) (1024, 4, 256) 0x04 307.2 2 4 (128,
2, 128), (128, 4, 256), (256, 2, 128), (256, 4, 256), (512, 2,
128), (512, 4, 256), (1024, 2, 128) (1024, 4, 256) 0x05 307.2 4 8
(512, 4, 128), (128, 4, 256), (1024, 4, 128), (256, 4, 256), (2048,
4, 128) (512, 4, 256), (1024, 4, 256), (2048, 4, 128) 0x06 614.4 1
4 (128, 1, 64), (128, 4, 256), (256, 1, 64), (256, 4, 256), (512,
1, 64), (512, 4, 256), (1024, 1, 64) (1024, 4, 256) 0x07 614.4 2 4
(512, 2, 64), (128, 4, 256), (1024, 2, 64), (256, 4, 256), (2048,
2, 64) (512, 4, 256), (1024, 4, 256), (2048, 4, 128) 0x08 921.6 2 4
(1024, 2, 64), (128, 4, 256), (3072, 2, 64) (256, 4, 256), (512, 4,
256), (1024, 4, 256), (2048, 4, 128), (3072, 2, 64) 0x09 1228.8 1 4
(512, 1, 64), (128, 4, 256), (1024, 1, 64), (256, 4, 256), (2048,
1, 64) (512, 4, 256), (1024, 4, 256), (2048, 4, 128) 0x0a 1228.8 2
4 (4096, 2, 64) (128, 4, 256), (256, 4, 256), (512, 4, 256), (1024,
4, 256), (2048, 4, 128), (3072, 2, 64), (4096, 2, 64) 0x0b 1843.2 1
4 (1024, 1, 64), (128, 4, 256), (3072, 1, 64) (256, 4, 256), (512,
4, 256), (1024, 4, 256), (2048, 4, 128), (3072, 2, 64) 0x0c 2457.6
1 4 (4096, 1, 64) (128, 4, 256), (256, 4, 256), (512, 4, 256),
(1024, 4, 256), (2048, 4, 128), (3072, 2, 64), (4096, 2, 64) 0x0d
1536.0 2 4 (5120, 2, 64) (128, 4, 256), (256, 4, 256), (512, 4,
256), (1024, 4, 256), (2048, 4, 128), (3072, 2, 64), (4096, 2, 64),
(5120, 2, 64) 0x0e 3072 1 4 (5120, 1, 64) (128, 4, 256), (256, 4,
256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128), (3072, 2, 64),
(4096, 2, 64), (5120, 2, 64) 0x0f N/A N/A N/A N/A NA 0x10 460.8 4 8
(1024, 4, 64), (128, 4, 256), (2048, 4, 64), (256, 4, 256), (3072,
4, 64) (512, 4, 256), (1024, 4, 256), (2048, 4, 128) 0x11 614.4 4 8
(1024, 4, 64), (128, 4, 256), (2048, 4, 64), (256, 4, 256), (4096,
4, 64) (512, 4, 256), (1024, 4, 256), (2048, 4, 128) 0x12 768.0 4 8
(1024, 4, 64), (128, 4, 256), (2048, 4, 64), (256, 4, 256), (5120,
4, 64) (512, 4, 256), (1024, 4, 256), (2048, 4, 128) 0x13 921.6 4 8
(2048, 4, 64), (128, 4, 256), (6144, 4, 64) (256, 4, 256), (512, 4,
256), (1024, 4, 256), (2048, 4, 128) 0x14 1075.2 4 8 (1024, 4, 64),
(128, 4, 256), (7168, 4, 64) (256, 4, 256), (512, 4, 256), (1024,
4, 256), (2048, 4, 128) 0x15 1228.8 4 8 (8192, 4, 64) (128, 4,
256), (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128)
0x16 1843.2 2 4 (2048, 2, 64), (128, 4, 256), (6144, 2, 64) (256,
4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128), (3072, 2,
64), (4096, 2, 64), (5120, 2, 64) 0x17 2150.4 2 4 (1024, 2, 64),
(128, 4, 256), (7168, 2, 64) (256, 4, 256), (512, 4, 256), (1024,
4, 256), (2048, 4, 128), (3072, 2, 64), (4096, 2, 64), (5120, 2,
64) 0x18 2457.6 2 4 (8192, 2, 64) (128, 4, 256), (256, 4, 256),
(512, 4, 256), (1024, 4, 256), (2048, 4, 128), (3072, 2, 64),
(4096, 2, 64) 0x19 3686.4 1 4 (2048, 1, 64), (128, 4, 256), (6144,
1, 64) (256, 4, 256), (512, 4, 256), (1024, 4, 256), (2048, 4,
128), (3072, 2, 64), (4096, 2, 64), (5120, 2, 64) 0x1a 4300.8 1 4
(1024, 1, 64), (128, 4, 256), (7168, 1, 64) (256, 4, 256, (512, 4,
256), (1024, 4, 2560, (2048, 4, 128), (3072, 2, 64), (4096, 2, 64),
(5120, 2, 64) 0x1b 4915.2 1 4 (8192, 1, 64) (128, 4, 256), (256, 4,
256), (512, 4, 256), (1024, 4, 256), (2048, 4, 128), (3072, 2, 64),
(4096, 2, 64), (5120, 2, 64)
[0092] In any active slot, the 1xEV-DO forward link 504 may
transmit from a base station 126-142 to an AT 202-240 using one of
the transmission formats listed in Table 1C.
[0093] If the present method and apparatus is implemented in a
wireless communication system employing the cdma2000 1xEV-DO
forward link standard, method 300 may make two pre-superposition
coding determinations at step 316. Using the first superposition
coding determination, method 300 may determine at 316 whether the
user 202 selected at step 312 (the most deserving user 202) has a
requested DRC of less than a low threshold data rate (e.g., 307.2
kbps for the 1xEV-DO forward link standard). If the user 202
selected at step 312 has a requested DRC of less than 307.2 kbps
for example, then a superposition coded packet may not be compiled
since any gain on the throughput data rate based on a superposition
coded packet may be negligible under such circumstances (due to
overhead incurred).
[0094] Using the second superposition coding determination, if the
user 202 selected at step 312 has a requested DRC approximately
equal to the maximum data rate for the given system (e.g., 3,072.0
kbps for the 1xEV-DO forward link 504 standard), then a
superposition coded packet is not compiled since any gain on the
throughput data rate based on a superposition coded packet may be
negligible under such circumstances. Thus, if any pre-superposition
coding criteria have not been met at step 316, method 300 may
proceed to step 318 where a superposition coded packet is not
compiled. Since the requested DRC of user 202 is 475.7 kbps (see
FIG. 8C), method 300 as applied to the present example may
determine at 316 that pre-superposition coding criteria have been
met (e.g. 307.2 kbps<most deserving user requested
DRC<3,072.0 kbps).
[0095] If there are no pre-superposition coding criteria at step
314 or if all the pre-superposition coding criteria have been met
at step 316, method 300 may proceed to step 320. At step 320, base
station 130 may determine whether to add other user 204-240 data
packets to the most deserving user 202 data packet as a
superposition coded packet. To achieve this, base station 130 may
compile a list of user 202-240 candidates for superposition coding
at step 322. The first user 202-240 candidate chosen may be the
user selected at step 312. A reason for this may be that
conventional systems presently serve this most deserving user 202.
By employing the user 202 selected at step 312 as the first
potential user candidate for superposition coding, the present
invention may be seamlessly incorporated into conventional systems
without diminishing the expected operations of that system.
[0096] One way to select the remaining user 204-240 candidates is
to select all remaining users 204-240. In the present example, this
would mean selecting users 204 through 240 of FIG. 6. A problem
with this approach is that it is unlikely that the lower ranked
users (here, users 224, 230, and 226--see FIG. 8C) would be able to
process a superposition coded packet in a timely manner. User 226,
for example, may need to decode and re-encode the superposition
packet nineteen times, a processing period that most likely would
extend beyond a 1.67 millisecond time slot. A better approach may
be to select the remaining user 204-240 candidates for
superposition coding based on the pre-selected goal of maximizing
the throughput transmission rate. This selection also minimizes the
overhead required in signaling.
[0097] In one embodiment, superposition coding is limited to four
users 202-240. At step 324, method 300 may select as user 202-240
candidates for superposition coding no more than four users 202-240
in descending order of their evaluation function F.sub.i(n). The
order of the evaluation functions F.sub.i(n) may be ranked by a
scheduler 714. From FIG. 8C, user 202 (F.sub.202(n)=45), user 204
(F.sub.204(n)=23), user 232 (F.sub.232(n)=22), and user 218
(F.sub.218(n)=20) may be selected as user 202-240 candidates for
superposition coding at step 324.
[0098] At first, it would seem that the superposition coded packet
may always be composed of the maximum number of users 202-240
(here, four users 202, 204, 218, 232) since the more superposition
coded users 202-240, the greater the gain in throughput data rate.
However, when implementing superposition coding, each participating
AT 202-240 receives certain information (like initial power
allocations and subsequent power updates) about the superposition
coded packet. This information takes up byte space in the
superposition coded packet to diminish the amount of bytes that may
be allocated to the payload data messages being transmitted. A
greater number of superposition coded users 202-240 may result in
more overhead (amount of preamble data that needs to be transmitted
as part of the superposition coded packet), thus decreasing the
data throughput rate. However, a smaller number of superposition
coded users 202-240 may result in a decreased data throughput rate.
Thus, to maximize the data throughput rate, method 300 anticipates
that the superposition coded packet may include a 2-user, 3-user,
or 4-user superposition coded packet depending upon the
circumstances.
[0099] It is noted that the term "users" refers to the
packet-oriented formats used in 1xEV-DO. Therefore, a if a
multi-user packet of 1xEV-DO is used, then, it would still be
treated as 1 user, with the parameters (DRC, etc) being determined
by the worst/weakest user within that multi-user packet.
[0100] At step 326, method 300 may eliminate from the user 204,
218, 232 candidates of step 324 those user candidates 204, 218, 232
who have a requested DRC that is less than the requested DRC of the
most deserving user 202 (e.g., the user 202 selected in step 312).
As shown in FIG. 8C, user candidates 204, 232, and 218 all have a
requested DRC that is greater than the 475.7 kbps requested DRC of
user 202. Thus, none of user candidates 204, 232, and 218 would be
eliminated in the present example.
[0101] At step 328, method 300 may determine whether any user
candidates 202, 204, 218, 232 of step 324 have identical requested
DRCs. If none of the user 202, 204, 218, 232 candidates of step 324
has identical requested DRCs, then method 300 may proceed to step
334. If any user 202, 204, 218, 232 candidates of step 324 have
identical requested DRCs, then method 300 may retain that step 324
user 202, 204, 218, 232 candidate with the highest average DRC
(e.g., max(DRC)) as step 330. At step 332, method 300 may eliminate
those remaining step 324 user 202, 204, 218, 232 candidates who had
identical requested DRCs as that user 204, 218, 232 retained in
step 330. As shown in FIG. 8C, user candidates 202, 204, 232, and
218 all have different requested DRCs, thus none of the user 202,
204, 218, 232 candidates of step 324 would be eliminated in the
present example.
[0102] At this point, it may be helpful to provide an overview of
steps 334 through 352. To select the 2-user, 3-user, or 4-user
combination that maximizes the throughput transmission rate, method
300 may compute the power allocations between the user 202, 204,
218, 232 candidates for superposition coding (step 334 through step
346). Method 300 may then determine a maximum transmission rate for
each user 202, 204, 218, 232 candidate combination (step 348). From
this, method 300 may select the user 202, 204, 218, 232 combination
that maximizes the throughput transmission rate (step 350). After
selecting the 2-user, 3-user, or 4-user combination that maximizes
the throughput transmission rate, method 300 may compile the
superposition coded packet from the selected user 202, 204, 218,
232 combination (step 352).
[0103] Power allocations between the user candidates for
superposition coding (step 334 through step 346) may be related to
the maximum transmission rate for each user 202, 204, 218, 232
candidate combination (step 348). To determine the maximum
transmission rate R.sub.i for each user 202, 204, 218, 232
combination, method 300 may employ the following equation:
R i = log 2 ( 1 + .alpha. i P T N i + j > i .alpha. j P T ) ( 3
) ##EQU00003##
[0104] where [0105] R.sub.i represents the maximum transmission
rate for each user 202, 204, 218, 232 combination; [0106] P.sub.T
represents the total power used to transmit a superposition coded
packet; [0107] .alpha. ("alpha") represents a scalar applied to the
total transmitted power P.sub.T; and [0108] N.sub.i represents the
noise spectral power density of the internal noise that may be
contributed by a base station 126-144 to an incoming signal.
[0109] Equation 3 may be written as:
R.sub.i=log.sub.2(1+(E.sub.b/N.sub.t)) (4) [0110] where E.sub.b is
the energy per bit; and [0111] where E.sub.b/N.sub.t is the energy
per bit per noise spectral power density and is related to the data
rate DRC through the SINR by the processing gain of the system.
[0112] The E.sub.b/N.sub.t portion of equation (4) may play a role
in determining the power allocations between the user 202, 204,
218, 232 candidates for superposition coding. To determine the
power allocations between the user 202, 204, 218, 232 candidates
for superposition coding, method 300 may employ the following
equations to obtain each a ("alpha") total transmission power
scalar:
(E.sub.b/N.sub.t).sub.drc,1<(E.sub.b/N.sub.t).sub.drc,2<(E.sub.b/N-
.sub.t).sub.drc,3<(E.sub.b/N.sub.t).sub.drc,4 (5)
[0113] where each (E.sub.b/N.sub.t).sub.drc is based on a requested
DRC, and
(E.sub.b/N.sub.t).sub.1=.alpha..sub.1.times.(E.sub.b/N.sub.t).sub.drc,1/-
[(1-.alpha..sub.1).times.(E.sub.b/N.sub.t).sub.drc,1+1] (6)
(E.sub.b/N.sub.t).sub.2=.alpha..sub.2.times.(E.sub.b/N.sub.t).sub.drc,2/-
[(1-.alpha..sub.1-.alpha..sub.2).times.(E.sub.b/N.sub.t).sub.drc,2+1]
(7)
(E.sub.b/N.sub.t).sub.3=.alpha..sub.3.times.(E.sub.b/N.sub.t).sub.drc,3/-
[(1-.alpha..sub.1-.alpha..sub.2-.alpha..sub.3).times.(E.sub.b/N.sub.t).sub-
.drc,3+1] (8)
(E.sub.b/N.sub.t).sub.4=.alpha..sub.4.times.(E.sub.b/N.sub.t).sub.drc,4/-
[(1-.alpha..sub.1-.alpha..sub.2-.alpha..sub.3-.alpha..sub.4).times.(E.sub.-
b/N.sub.t).sub.drc,4+1] (9)
[0114] Method 300 may begin determining the power allocations
between the user 202, 204, 218, 232 candidates for superposition
coding at step 334. The power allocations between the user 202,
204, 218, 232 candidates for superposition coding may be determined
by computing the .alpha. ("alpha") scalar for each remaining user
202, 204, 218, 232 candidate.
[0115] Terminals 202-240 far away from the base station 126-144
require a higher transmit power level at the base station 126-144
to achieve the same data rate as that for terminals 202-240 close
to the base station 126-142 in order to overcome the additional
path loss. In a 2-user superposition coded packet where 20 watts
are available as the total transmitted power, a weak user 202-240
may require 19 watts of total transmitted power and a strong user
202-240 may require 1 watt of total transmitted power. Method 300
may achieve this shouting and whispering through the alpha .alpha.
scalar.
[0116] Preferably, method 300 assigns the .alpha. ("alpha") scalar
from the most deserving user 202 to the strongest user 212 based on
their respective requested DRC. FIG. 8B illustrates the most
deserving user 202 to the strongest user 212 based on the requested
DRC being ranked as follows for the remaining user candidate: user
202, user 218, user 232, and user 204. Thus, method 300 may begin
by determining the power allocation of the most deserving user,
here user 202.
[0117] To determine the power allocation to the most deserving user
202, method 300 may set a data rate at step 336 at which the most
deserving user 202 (namely, the user 202 selected at step 312) may
be served when a superposition coded packet is employed. For the
1xEV-DO forward link standard, the served data rate for the most
deserving user 202 in the superposition coded packet may be the
greater of 153.6 kbps and the most deserving user's 202 DRC divided
by the number of users 202, 204, 218, 232 in the superposition
coded packet. This may be written as:
Served Data Rate.sub.(most deserving user)=max(153.6
kbps,(DRC.sub.(most deserving user)/number of SP users)) (10)
[0118] In the example of FIG. 8C, the requested DRC of the most
deserving user (user 202) is 475.7 kbps. Applying equation 10,
Served Data Rate.sub.(most deserving user)=max (153.6 kbps,
475.7/2, 475.7/3, 475.7/4), or Served Data Rate.sub.(most deserving
user)=max (153.6 kbps, 237.9 kbps, 158.6 kbps, 118.9 kbps), or
Served Data Rate.sub.(most deserving user)=237.9 kbps.
[0119] Knowing the Served Data Rate.sub.(most deserving user) and
the requested DRC for the most deserving user 202 (from e.g., FIG.
8C), method 300 may employ equations to determine the .alpha.
("alpha") scalar for a user candidate at step 338. In the present
example, method 300 may employ equation (6) above to determine the
.alpha. ("alpha") scalar for the most deserving user 202. For user
202, the Served Data Rate was calculated from equation (10) as
237.9 kbps and the requested DRC from FIG. 8C is 475.7 kbps. Thus,
for user 202, the .alpha..sub.202 ("alpha") scalar may be
calculated from equation (6) as:
(E.sub.b/N.sub.t).sub.1=.alpha..sub.1.times.(E.sub.b/N.sub.t).sub.drc,1/-
[(1-.alpha..sub.1).times.(E.sub.b/N.sub.t).sub.drc,1+1] (6)
substituting,
(E.sub.b/N.sub.t).sub.202=.alpha..sub.202.times.(E.sub.b/N.sub.t).sub.dr-
c,202/[(1-.alpha..sub.202).times.(E.sub.b/N.sub.t).sub.drc,202+1]
(6a)
237.9 kbps=.alpha..sub.202.times.475.7
kbps/[(1-.alpha..sub.202).times.(475.7 kbps+1] (6b)
.alpha..sub.202=0.9958(=.alpha..sub.1) (6c)
[0120] At step 340, method 300 may determine whether an alpha
shortage has occurred. An alpha shortage is where the sum of all
alphas is equal to or greater than one. If an alpha shortage has
occurred, then method 300 may assign the remaining alpha to the
strongest user 202 at step 342 and may drop users 204, 218, 232
just above the primary user or strongest user 202 at step 344. This
maximizes the total throughput. The method 300 then may proceed to
step 348.
[0121] If an alpha shortage has not occurred, then method 300 may
determine at step 346 whether there are any remaining user
candidates 204, 218, 232 for which an alpha has not been
calculated. If there are remaining user 204, 218, 232 candidates
for which an alpha has not been calculated, method 300 returns to
step 338. For the next strongest user 218, the .alpha..sub.218
("alpha") scalar may be calculated from equation (7) since
.alpha..sub.1 (here, .alpha..sub.202) has been calculated from
equation (6). The .alpha..sub.232 scalar and the .alpha..sub.204
scalar similarly may be determined from equation (8) and equation
(9) respectively. If an alpha has been calculated for each user
202, 204, 218, 232 candidate, method 300 may proceed to step
348.
[0122] Method 300 may begin to determine the maximum transmission
rate for each user 2-user, 3-user, and 4-user combination at step
348. Recall that the maximum transmission rate R.sub.i for each
user 202, 204, 218, 232 combination, method 300 may employ the
following equation:
R i = log 2 ( 1 + .alpha. i P T N i + j > i .alpha. j P T ) ( 3
) ##EQU00004##
[0123] For user 202, 204, 218, 232 candidates 1, 2, 3, and 4,
method 300 may employ the following equations to determine the
maximum transmission rate for each user 202, 204, 218, 232
candidate combination:
R 4 = log 2 ( 1 + .alpha. 4 P T N 4 ) ( 11 ) R 3 = log 2 ( 1 +
.alpha. 3 P T N 3 + .alpha. 4 P T ) ( 12 ) R 2 = log 2 ( 1 +
.alpha. 2 P T N 2 + .alpha. 3 P T + .alpha. 4 P T ) ( 13 ) R 1 =
log 2 ( 1 + .alpha. 1 P T N 1 + .alpha. 2 P T + .alpha. 3 P T +
.alpha. 4 P T ) ( 14 ) ##EQU00005##
[0124] Each of the variables in equations (11) through (14) may be
known at this point in the process. The alpha .alpha. power
transmission scalar for each user 202, 204, 218, 232 candidate may
have been determined during step 334 through step 346. The total
transmission power P.sub.T typically may be assigned by the
wireless communication system. The noise spectral power density N
for each user 202, 204, 218, 232 candidate is the internal base
station noise that may be contributed by a base station 126-142 to
each user 202, 204, 218, 232 candidate's incoming signal and thus
is known (possibly through the DRC requested). By employing
equations (11) through (14), the maximum transmission rate for each
user 202, 204, 218, 232 candidate combination may be determined at
step 348.
[0125] At step 350, method 300 may select the user 202, 204, 218,
232 combination that maximizes the throughput transmission rate.
For example, if R.sub.2=70 kbps for a 2-user superposition coded
packet, R.sub.3=80 kbps for a 3-user superposition coded packet,
and R.sub.4=75 kbps for a 4-user superposition coded packet, method
300 may select the 3-user superposition coded packet since the
3-user superposition has the largest kbps and thus maximizes the
throughput transmission rate.
[0126] At step 352, method 300 may compile the superposition coded
packet from the selected user 202, 204, 218, 232 combination. The
superposition coded packet may include a payload and a preamble.
The payload may include each data packet for the users 202, 204,
218, 232 included in the selected user 202, 204, 218, 232
combination. The preamble (or address header) may convey
superposition coded parameters of the packet and non-superposition
coded parameters of the packet.
[0127] The process of power allocation has been explained in an
example where the layers are either CDMA or OFDM (all data tones in
a particular layer are allocated to a particular user/multi-user
packet (MUP)). In case the lowest layer is CDMA and the second
layer is OFDMA, with groups of tones allocated to different users,
the power allocation for the lowest layer remains identical to that
described above. However, the second layer can follow an OFDMA
allocation policy, which jointly determines the power and tone
allocation to the set of chosen users, depending on the target rate
for the users. The final packet structure resembles FIG. 9F.
[0128] Superposition coded packet parameters may include: (a) the
number of users 202, 204, 218, 232 in the superposition coded
packet; (b) the length (nominal # of interlace slots) of the
superposition coded packet; (c) the fractional power allocation (a)
for each superposition coded packet user "i"; (d) the payload size
for each superposition coded packet user 202, 204, 218, 232; (e)
the physical address of each superposition coded user 202, 204,
218, 232; and (f) an indicator of whether the packet is a
single-user data packet, a multi-user data packet, or a multi-user,
superposition coded packet.
[0129] A two bit code may be needed to indicate the number of users
(2=01.sub.2, 3=10.sub.2, 4=11.sub.2) in the superposition coded
packet. The length (nominal # of interlace slots) of the
superposition coded packet also may be indicated by two bits of
code. The fractional power allocation (.alpha..sub.i) for each
superposition coded packet user "i" may be conveyed by 3-bits and
the payload size (the type of packet) for each superposition coded
packet user may be conveyed by 2-bits. Seven bits may be allocated
to convey a physical address (e.g., Medium Access Control
Identifier (MAC ID)) of each superposition coded user.
[0130] An AT 202-240 may utilize the number of users 202, 204, 218,
232 to determine whether the packet is a single-user data packet
(00.sub.2) or a multi-user packet (01.sub.2, 10.sub.2, 11.sub.2).
If the packet is a multi-user packet, then the AT 202-240 may
utilize the power allocation to distinguish between a multi-user
data packet and a multi-user, superposition coded packet. A
multi-user data packet always is transmitted at full power
(P.sub.T) and a multi-user, superposition coded packet is
transmitted by scaled power (.alpha.P.sub.T).
[0131] Other packet parameters (non-superposition coded packet
parameters) may be conveyed by the preamble depending on the
communication standard in which the present method and apparatus is
employed. In order to incorporate the superposition coding
strategy, the preamble may distinguish the superposition coded
packet from the other types of data packets, such as single user
packet, multi-user packet, control channel packet, and broadcast
packet.
[0132] Conveying preamble information is viewed as overhead in that
packet bit space allocated preamble information takes away packet
bit space that may be allocated to the payload. As discussed in
more detail below, the most deserving user 202 may process the
superposition coded packet without information regarding the
superposition coded packet parameters. Thus, the superposition
coded packet may be compiled such that the most deserving user 202
may not receive any superposition coded packet parameter
information in the preamble, but still may receive
non-superposition coded packet parameters in the preamble. Table 2
below illustrates an example superposition coded packet structure
for a 3-user superposition coded packet with the bit allocation
shown in parenthesize:
TABLE-US-00004 TABLE 2 EXAMPLE 3-USER SUPERPOSITION CODED PACKET
STRUCTURE non-SPC USER Superposition Coded (SPC) Packet Parameters
parameters Payload #1 (0) non-SPC Data Packets parameters 1(4096)
(20) 2(1024) 3(1024) #2 # MAC .alpha..sub.1 Payload MAC
.alpha..sub.2 Payload MAC .alpha..sub.3 Payload non-SPC Data
Packets SPC ID SP (3) size ID SP (3) size ID SP (3) size parameters
1(4096) Users #1 (2) #2 (2) #3 (2) (20) 2(1024) (2) (7) (7) (7)
3(1024) #3 # MAC .alpha..sub.1 Payload MAC .alpha..sub.2 Payload
MAC .alpha..sub.3 Payload non-SPC Data Packets SPC ID SP (3) size
ID SP (3) size ID SP (3) size parameters 1(4096) Users #1 (2) #2
(2) #3 (2) (20) 2(1024) (2) (7) (7) (7) 3(1024)
[0133] Each of these packets can be constructed using a different
wireless communication standard.
[0134] FIG. 9A is a logic block diagram 500 of the apparatuses used
to compile, transmit, process and receive a superposition coded
packet. Individual data packets may be encoded in encoders 14a-14d
respectively, modulated in modulators 17a-17d respectively,
transmission power (alpha ".alpha.") scaled (namely,
.alpha..sub.iP.sub.T) by multiplying the encoded and modulated data
packets by a applied to the total transmitted power P.sub.T, in
multipliers 18a-18d respectfully. The resultant packets are then
added together in adder 520 to compile a superposition coded packet
in transmitter 502. The superposition coded packet may then be
transmitted over each forward link channel 504a-504d. Each AT 202,
204, 218, 232 may then receive and process the superposition coded
packet in receiver demodulators 508a-508d and decoders 510a-510d
respectfully found in receivers 506a-506d respectfully. To process
a superposition coded packet, the decoder 510a-510b treats the data
packets for stronger users 202, 204, 218, 232 as interference and
(ii) decodes and subtracts out data packets meant for weaker users
202, 204, 218, 232.
[0135] FIG. 9B is an example which elaborates on transmitter 502 of
FIG. 9A, where the various users 202, 204, 218, 232 utilize
different wireless communication standards in order to achieve
better spectral efficiency. In one case the most deserving user 202
utilizes a 1xEV-DO Rev B format and other users 204, 218, 232
utilize OFDM packet formats. FIG. 9B shows, for example, Data
Packet 1 encoded with an a 1xEV-DO Rev B format, while data packets
2 through 4 are encoded using utilizing an OFDM format. FIG. 9B
also shows an inverse Fourier transform (IFFT) applied by digital
signal processors (DSP) 16a-16d to OFDM pilot tones and to the
frequency domain symbols produced by encoders 14b-14d producing
digital time-domain OFDM symbols. DSPs 16a-16d may also perform
additional spectral shaping on the digital time-domain OFDM symbols
and add a cyclic prefix or guard interval. In addition, data
packets are transmission power (alpha ".alpha.") scaled (namely,
.alpha..sub.iP.sub.T) by multiplying them by a applied to the total
transmitted power P.sub.T, in multipliers 18a-18d respectfully. The
OFDM pilot tones are scaled by multiplying them by beta .beta.
applied to the total transmitted power P.sub.T, in multiplier 18e.
FIG. 9B also shows a 1xEV-DO formatted data packet 1 being combined
with the processed OFDM Pilot tones in summer 522. As illustrated
in FIG. 9B, packet 1 may be a 1xEV-DO data packet or a 1xEV-DO
control channel packet.
[0136] The four data packets are then combined in summer 520. The
output of summer 520 is input to multiplexer 524 along with an
1xEV-DO pilot, a MAC and a preamble signal to produce the
superposition coded packet.
[0137] FIGS. 9C and 9D provide an example of the data content in
the time and frequency domains. FIG. 9C shows how the various
packets are fit in the time-domain, with each user 202-240
receiving a fraction of the power. With layered coding, the base
stream is encoded and modulated in accordance with a first mode to
generate a first modulation symbol stream, a second stream is
encoded and modulated in accordance with a second mode to generate
a second modulation symbol stream and so on. The first and second
modes may be the same or different. The multiple modulation symbol
streams are then combined to obtain one data symbol stream.
Additional layers, like the MIMO-pilot may also be
accommodated.
[0138] FIG. 9C illustrates a mixed slot containing data using
different packet formats. The base stream is shown in as a layer
comprising 16 pilot tones. The first layer of the time slot
contains no useful OFDM content, and the second and third layers
use an OFDM format. In one embodiment, the first layer may be
encoded with an 1xEV-DO Rev B format. It is called a mixed slot
because data for one or more physical channels may be channelized
with different formats. In this embodiment, the first layer may be
added to the two OFDM waveforms to generate a composite waveform
that is transmitted in the mixed slot. The example in FIG. 9C is
used to illustrate that the various users 202-140 may use different
wireless communication standards to construct their data
packets.
[0139] FIG. 9D illustrates a 1xEV-DO forward link slot format used
in one embodiment of the present method and apparatus. As shown,
this slot format supports four channels: pilot, MAC, control, and
traffic. These are time-multiplexed within each slot (1.66 . . .
ms) as shown in FIG. 9D.
[0140] The pilot channel carries no information but is used to aid
in the detection, synchronization, and demodulation of the signal
at the receiver end. The MAC channel uses CDMA (it employs Walsh
codes of length 64) and carries control information (such as power
control bits) to individual access terminals 202-240.
[0141] The remaining parts of the slot are used for data,
transmitting either the control or traffic channel. As shown, the
control channel carries control information, transmitted
periodically, broadcast to mobile phones. The traffic channel
carries packets of user data. The traffic or data channel is a
mixed slot containing data using different packet formats. The base
stream is shown as a layer comprising MIMO-pilot tones which is
scaled by scaling factor .beta.. The next three layers are data or
traffic streams. The first layer uses a 1xEV-DO Rev B packet
format, and the second and third layers use an OFDM format. The
scaling factor .alpha. for each user is shown as .alpha..sub.1,
.alpha..sub.z, .alpha..sub.3, and .alpha..sub.4. Four data
channels, each containing 400 chips is shown. In the first data
channel, the first 128 chips are reserved for the preamble while
the other 272 chips are used for the 1xEV-DO data chips and the
OFDM tones. In the three other data channels, 400 chips are used
for the 1xEV-DO data chips and the OFDM tones. The MIMO pilot tones
may be present (.beta..noteq.0) in order to assist channel
estimation in multi-antenna systems. This is not related to the
present embodiment, but is included to faithfully describe a
practical system. When the MIMO pilot is present, all layers are
going to treat it as interference.
[0142] FIG. 9E illustrates a mixed data slot using different packet
formats. The base stream is shown in as a layer comprising MIMO
pilot tones. The first layer of the time slot uses a 1xEV-DO packet
format, and the second and third layers use a OFDM format. In this
embodiment, the first layer may be added to layers 2 and 3 to
generate a composite waveform that is transmitted in the mixed
slot.
[0143] FIG. 9G illustrates another mixed data slot using different
packet formats. The base stream is shown in as a layer comprising
MIMO pilot tones. The first layer of the time slot uses a GSM
format and the second layer use a OFDM format. In this embodiment,
the first layer may be added to layer 2 to generate a composite
waveform that is transmitted in the mixed slot.
[0144] FIG. 10 is a method 600 to compile, transmit, and process
one or more data packets. Base station 130 may determine whether to
compile a single-user data packet, a multi-user data packet
transmitted at full power, or a multi-user, superposition coded
packet transmitted by scaled power (.alpha.P.sub.T). At step 602,
base station 130 may determine whether to compile a superposition
coded packet transmitted by scaled power (.alpha.P.sub.T). Base
station 130 may make this determination based on method 300. If
base station 130 decides to compile a single-user data packet or a
multi-user data packet transmitted at full power, method 600 may
proceed to step 604 where base station 130 may compile the desired
data packet. From step 604, method 600 may proceed to step 608.
[0145] If base station 130 decides at step 602 to compile a
multi-user, superposition coded packet, method 600 may proceed to
step 606. At step 606, method 600 may compile the superposition
coded packet from a selected user 202-240 combination. This may be
achieved by employing method 300. At step 608, method 600 may
transmit the superposition coded packet over a forward link channel
504 to each user 202-240 in the selected user 202-240 combination.
Each user in the selected user 202-240 combination may receive the
superposition coded packet at step 610.
[0146] In the present example, assume that data packets for all
four users 202, 204, 232, and 218 are contained within the
superposition coded packet. For a user 202, 204, 232, and 218 to
obtain the data packet meant for that user 202, 204, 232, and 218,
the user may process the superposition coded packet. Thus, at step
612, each user 202, 204, 232, and 218 may begin processing the
received superposition coded packet.
[0147] As a first step in processing the received superposition
coded packet, each user 202, 204, 232, and 218 may read the
preamble at step 614. As noted above, the most deserving user 202,
204, 232, and 218 need not receive any superposition coded packet
parameter information in the preamble to process the superposition
coded packet.
[0148] At 616, each user may determine whether that user 202, 204,
232, and 218 is the most deserving user 202. For example, if the
received preamble contains superposition coded packet parameters
(the MAC ID), then that user 202, 204, 232, and 218 may know that
it is not the most deserving user 202 and method 600 may proceed to
step 622. If the received preamble does not contain any
superposition coded packet parameters, then that user 202, 204,
232, and 218 may know it is the most deserving user 202. In one
embodiment, the super-position coded packet contains a multi-user
packet which is transmitted to the most deserving user with less
than 100% power allocation. This multi-user packet also contains
information about the superposed users 202, 204, 232, and 218 and
their payload size and initial power allocation.
[0149] If a user 202, 204, 232, and 218 determines that it is the
most deserving user 202 at step 616, then that user 202, 204, 232,
and 218 may attempt to process the received packet at 618 by
assuming that one hundred percent of the total transmitted power
was allocated to the most deserving user 202. If ultimately
successful, then this means that the received packet was either a
single-user data packet (.alpha.=1.00), a multi-user data packet
transmitted at full power (.alpha.=1.00), or a superposition coded
packet in which the disparity between the most deserving user's
202, 204, 232, and 218 SINR and the next most deserving user's 204,
232, and 218 SINR was so large that nearly all of the transmitted
power was allocated to the most deserving user 202. The most
deserving user 202 also may attempt to process the received packet
at 620 by assuming that sixty percent of the total transmitted
power was allocated to the most deserving user 202. From step 618
and 620, method 600 may proceed to step 622.
[0150] To process a superposition coded packet at step 622, a user
(i) treats the data packets for stronger users 202, 204, 218, 232
as interference and (ii) decodes and subtracts out data packets
meant for weaker users 202, 204, 218, 232. By subtracting out
weaker user 202, 204, 218, 232 data packets, each user may obtain
the data packet intended for that user 202, 204, 218, 232.
[0151] Treating data packets as interference and canceling such
data packets may be achieved by successive interference
cancellation. In Successive Interference Cancellation (SIC), each
user's 202, 204, 218, 232 signal may be demodulated and canceled in
order from the most deserving signal to the strongest signal
according to their scaled transmission power (.alpha..sub.iP.sub.T)
value. The scaled transmission power value is known since each
scaled transmission power value is transmitted as part of the
preamble to the superposition coded packet. The successive
cancellations of the interference may be carried out as follows:
[0152] i) Recognize the weaker signal(s); [0153] ii) Decode the
weaker user(s) 202, 204, 218, 232; [0154] iii) Determine the
amplitude of the decoded user 202, 204, 218, 232 from the
superposition coding parameters; [0155] iv) Regenerate
(re-construct or re-encode) the weaker user(s)' 202, 204, 218, 232
signal. This re-construction should take into account the wireless
communication standard that was used in constructing the data
packet for the corresponding weaker user 202, 204, 218, 232; [0156]
v) Cancel the weaker user 202, 204, 218, 232; and [0157] vi) Repeat
until all weaker users 202, 204, 218, 232 are decoded.
[0158] Thus, to process the superposition coded packet at step 622,
method 600 may cancel out stronger user(s) 202, 204, 218, 232 data
packets at step 624 and subtract out weaker user 202, 204, 218, 232
data packets at step 626 to process a superposition coded packet.
In the present example, user 202 treat all other users 202, 204,
218, 232 as interference since user 202 is the most deserving user
202. Table 3 below identifies the technique each of users 202, 204,
232, and 218 may employ to obtain the desired data packet from the
superposition coded packet:
TABLE-US-00005 TABLE 3 SUPERPOSITION CODED PACKET PROCESSING
PACKETS USERS PAC 218 PAC 232 PAC 204 PAC 202 USER 202 Treat as
interference (-) USER 204 treat as interference (-) Subtract USER
232 treat as (-) subtract Subtract interference USER 218 (-)
subtract subtract Subtract
[0159] During the processing of a data packet, an AT decoder 506
may correctly process the data packet. Alternatively, the AT
decoder 506 may detect errors and be unable to process the data
packet correctly. In either case, the AT 202, 204, 218, 232 may
send an Acknowledgement (positive or negative) to the base station
126-142 to inform the base station 126-142 of the ATs 202, 204,
218, 232 success in processing a data packet. However, this may not
be used with a super position coded information packet. In one
embodiment, an on-off keying modulation (OOK) ACK (similar to that
used for MUP) may be used, where a 1 implies an ACK (positive
acknowledgement) and a 0 implies a NAK (negative
acknowledgement).
[0160] Automatic Repeat Request (ARQ) schemes provide for an
automatic retransmission of data. Hybrid ARQ (H-ARQ) systems allow
for early termination of such retransmissions when data is decoded
correctly. The receiver AT 202, 204, 218, 232 may inform the
transmitter base station 126-142 as to whether the base station
126-142 needs to re-send a data packet to that particular AT 202,
204, 218, 232. A positive Acknowledgement (ACK) may be returned
when the data is received correctly and a Negative Acknowledgement
(NACK) may be returned when an error is detected. A negative
acknowledgement may be silence (no return ARQ) and a positive
acknowledgement may be a return ARQ. In a more complex error
control system, information blocks may be encoded for partial error
correction at the AT 202, 204, 218, 232 receiver and additional,
uncorrected errors may be retransmitted by the base station
126-142. Method 600 may utilize a variety of error control systems
and each user AT 202, 204, 218, 232 may send an ARQ back to the
base station 126-142 at step 628.
[0161] At step 630, base station 130 may receive each ARQ from the
superposition coded packet users 202, 204, 218, 232. Recall that
the total transmit power (P.sub.T) behind the superposition coded
packet is allocated to each data packet contained in the
superposition coded packet based on the alpha .alpha. scalar
(namely, .alpha..sub.iP.sub.T). If a user 202, 204, 218, 232
correctly receives data from a data packet, then the base station
130 need not resend that user its particular data packet. Thus, if
a user 202, 204, 218, 232 terminates their request for
re-transmission of a data packet before the last slot of the slot
interlace, the transmit power originally allocated to that user
202, 204, 218, 232 may be redistributed among the remaining users
202, 204, 218, 232. This may be referred to as dynamic alpha
updating.
[0162] During each interlace slot, method 600 may re-send those
data packets for which an NACK-ARQ was received. Table 4 below
illustrates an example 4-slot interlace:
TABLE-US-00006 TABLE 4 ##STR00001##
[0163] The users 202, 204, 218, 232 listed in Table 4 are arranged
from the most deserving user 202 (lowest reported SINR) to the
strongest user 218 (highest reported SINR). After the completion of
the first interlace slot, user 2 (user 204) correctly received data
from the superposition coded packet and the remaining users 202,
218, 232 (1, 3, and 4) experienced errors. A reason user 2 (204)
correctly received data from the superposition coded packet after
the first interlace slot may be that user 2 (204) had better
forward link channel than predicted.
[0164] Base station 130 may allocate the transmission power for
user 2 (user 204) to user 3 (user 232) as indicated by the arrow in
Table 4. After the second interlace slot, user 4 (218) correctly
received data. Thus, base station 130 allocated the transmission
power for early terminating user 4 (218) to the user who both
experienced errors and requested the next highest SINR, namely user
3 (232). After the third interlace slot, user 3 (232) correctly
received data and base station 130 allocated the transmission power
for user 3 (232) to user 1 (202).
[0165] In view of the above, method 600 may determine at step 632
whether all users 202, 204, 218, 232 correctly received the data
from their data packet. If all users 202, 204, 218, 232 correctly
received the data from their data packet, then method 600 may
proceed to step 638 and terminate. If all users 202, 204, 218, 232
did not correctly receive the data from their data packet, then
method 600 may identify at step 634 those users 202, 204, 218, 232
who correctly received the data from their data packet. For each
successful decoding user identified in step 634, method 600 may
reallocate at step 636 the power transmission of each successful
decoding user 202, 204, 218, 232 to the unsuccessful decoding user
202, 204, 218, 232 having the next higher SINR. Method 600 then may
return to step 602 and compile a data packet for the next time slot
interlace.
[0166] On returning to step 602, base station 130 may determine
whether to compile a single-user data packet or a multi-user,
superposition coded packet based on the ARQs received by base
station 130 in step 630. If only one user 202, 204, 218, 232
experienced errors in decoding its data packet, then base station
130 need only compile a single-user data packet. Moreover, in
compiling the data packet for the next time slot interlace, some of
the preamble bits may be discarded since there may be less data
packets to send during the particular time slot interlace.
Discarding preamble bits may reduce the amount of data to be
transmitted and therefore increase the rate at which that data may
be transmitted. Method 600 may repeat in this fashion until all
users 202, 204, 218, 232 correctly receive the data from their data
packet.
[0167] As disclosed above, an early termination due to ARQ may
result in power reallocation. On a layer level, transmission for
layer 2 will terminate early only if all layer 2 users acknowledge
receipt of their packet. Likewise, transmission for layer 1
terminates only if all layer 2 users and layer 1 users acknowledge
receipt of their packet. The demodulated SINR is measured using
embedded OFDM pilot tones. Thus, if one of the packets in layer 2,
for example, is decoded, power allocation to other layers is
detected due to these embedded OFDM pilot tones.
[0168] It is noted that an AT 202, 204, 232 and 218 may determine
that a packet is superposition coded after the multi-user packet is
decoded.
[0169] The present method and apparatus may be embodied in a
computer chip for the base station 126-142 to address the
compiling, transmitting, and retransmitting of a superposition
coded packet and a computer chip for each AT 202-240 to address the
processing of a received superposition coded packet 126-142. This
may require invoking the scaling and adding features of an existing
base station computer chip and including a decoder, subtractor, and
re-encoder in existing AT 202-240 computer chips. The method and
apparatus may be employed each time the base station 126-142
computer chip compiles a superposition coded packet, where the
owner of the present method and apparatus may charge a fee each
time the base station 126-142 computer chip compiles a
superposition coded packet.
[0170] In one embodiment, the superposition coded packet may be
limited to two layers, which may be an example of two layer OFDMA
superposition coding or 2-layer OFDMA-SPC (See FIG. 11). FIG. 11 is
an example of two layer OFDMA superposition coding packet with a
nominal span equal to two slots. It has a maximum of 2-layers which
simplifies terminal interference cancellation. In addition, it may
use OFDMA in the higher layer which simplifies power re-allocation.
Thus, when decoding the lowest layer, layer 2 is treated as
interference. In FIG. 9H, .alpha..sub.1 indicates the power
allocated to the lowest layer, while .alpha..sub.2 indicates the
power allocated to layer 2 where the power allocation is split
amongst the tones (up to 4 packets in layer 2).
[0171] The lower layer may utilize a 1xEV-DO multi-user format and
the higher layer may utilize an OFDM packet format. In one
embodiment, the lower layer uses 1xEV-DO Rev A/B multi-user packet.
FIG. 9H illustrates the higher layer with two users allocated 50%
of the bandwidth each. However, in another embodiment, up to four
users served on the higher layer.
[0172] The lowest layer may be a 1xEV-DO or control channel packet.
The preamble power allocation may be equal to the power allocated
for the lowest layer data transmission. It is noted that an AT 202,
204, 232 and 218 may determine that a packet is superposition coded
after the multi-user packet is decoded.
[0173] A MAC-ID is used to indicate that the packet is a
superposition coded information packet. Also, it uses 2 bits to
indicate the number of packets in layer 2, (i.e., 1, 2, 3, or 4 in
one embodiment) and 2 bits to indicate the packet termination
target.
[0174] In addition, layer 2 uses two bits to indicate the number of
users in layer 2. Also, it uses an eight bit MAC index, four bits
to convey the assigned distributed tone sets/user, four bits to
convey initial power allocation (same across all assigned tones)
and payload size may be conveyed by four bits also.
[0175] FIG. 12 is a computer system 700 with which some embodiments
of the invention may be implemented. In some embodiments, the
techniques of the present invention may be hard-coded into hardware
devices dedicated specifically for graphics production and/or
implemented in computer executable instructions stored in a
computer readable medium (software).
[0176] The computer system 700 may include a bus 705, a processor
710, a system memory 715, a read-only memory 720, a permanent
storage device 725, input devices 730, output devices 735, and an
alternative processor 740. Some or all of the items of computer
system 700 may be included in a compiling unit or included in a
control processor.
[0177] The bus 705 may collectively represent all system,
peripheral, and chipset buses that communicatively connect the
numerous internal devices of the computer system 700. For instance,
the bus 705 may communicatively connect the processor 710 with the
read-only memory 720, the system memory 715, and the permanent
storage device 725.
[0178] The Read-Only-Memory (ROM) 720 may store static data and
instructions which may be needed by the processor 710 and other
modules of the computer system. The permanent storage device 725,
on the other hand, may be a read-and-write memory device. This
device may be a non-volatile memory unit that stores instruction
and data even when the computer system 700 may be off Some
embodiments of the invention may utilize a mass-storage device
(such as a magnetic or optical disk and its corresponding disk
drive) as the permanent storage device 725. Other embodiments may
utilize a removable storage device (such as a floppy disk or other
storage disk, and corresponding disk drive) as the permanent
storage device.
[0179] Like the permanent storage device 725, the system memory 715
may be a read-and-write memory device. However, unlike storage
device 725, the system memory may be a volatile read-and-write
memory, such as a random access memory (RAM). The system memory may
store some of the instructions and data that the processor needs at
runtime.
[0180] In some embodiments, instructions and/or data needed to
perform methods of the present patent application may be stored in
the system memory 715, the permanent storage device 725, the
read-only memory 720, or any combination of the three. For example,
the various memory units may contain instructions of an application
and/or graphics data generated by the application. For example, the
steps illustrated in FIGS. 7 and 10 may be stored as instructions
stored in the system memory 715, the permanent storage device 725,
the read-only memory 720, or any combination of the three. In some
embodiments, the system memory 715 and/or the permanent storage
device 725 may comprise a cache and/or buffer.
[0181] From these various memory units, the processor 710 may
retrieve instructions to execute and data to process to perform the
processes of the present invention. In some embodiments, the
processor 710 may utilize an on-chip cache 712 to hold data
recently accessed or produced by the processor 710. In some
embodiments, the alternative processor 740 may execute instructions
and processes data to perform the processes of the present
invention. In one embodiment, the processor may comprise scheduler
714. The scheduler 714 may also be located in alternative processor
740 or as a separate processing means.
[0182] The bus 705 also may connect to the input and output devices
730 and 735. The input devices 730 may enable a user to communicate
information and select commands to the computer system 700. The
input devices 730 may include alphanumeric keyboards and
cursor-controllers. The output devices 735 may print or display
images generated by the computer system 700. The output devices may
include printers and display devices, such as Cathode Ray Tubes
(CRT) or Liquid Crystal Displays (LCD).
[0183] Finally, as shown in FIG. 12, the bus 705 also may couple
the computer system 700 to a network 765 through, for example, a
network adapter (not shown). In this manner, the computer system
700 may be a part of a network of computers (such as a Local Area
Network ("LAN"), a Wide Area Network ("WAN"), or an Intranet) or a
network of networks (such as the Internet). Any or all of the
components of the computer system 700 may be used in conjunction
with the present invention. However, one of ordinary skill in the
art would appreciate that any other system configuration also may
be used in conjunction with the present invention.
[0184] The method and apparatuses of FIGS. 7 and 10 described above
are performed by corresponding means plus function blocks
illustrated in FIGS. 13 and 14 respectively. In other words, steps
302 to 352 of FIG. 7 correspond to means plus function blocks 1302
to 1352 in FIG. 13. Likewise, steps 602 to 638 of FIG. 10
correspond to means plus function blocks 1602 to 1638 in FIG.
14.
[0185] The above method and apparatus is expected to provide
throughput gains in a variety of systems, including Evolution-Data
Only (Time Division Multiplexing) (EV-DO (TDM)), Orthogonal
Frequency Division Multiplexing (OFDM (TDM OFDM)), and 1x Code
Division Multiplexing (1x-CDM). The largest throughput gains are
expected for strong users operating in time (or
frequency)-orthogonal systems
[0186] The above method and apparatus may be applied to a variety
of applications. For example, when applied to the
Voice-Over-Internet Protocol (VoIP), the inventive superposition
coding on the 1x-EV-DO forward link may allow for lower latencies
(reduced transmission delays), a greater number of users per sector
(namely, a higher capacity), or a combination of the two. When
applied to broadcast services such as advertising, the broadcast
services may be superposition coded with unicast traffic directed
to an individual user so that both broadcast and unicast traffic
may be transmitted together. Thus, unlike conventional wireless
communication systems, the present invention minimizes or
eliminates the need to preempt broadcast traffic with unicast
traffic. In other words, broadcast traffic need not be compromised
during periods of unicast traffic for those systems employing the
present method and apparatus.
[0187] While the present method and apparatus has been described
with reference to numerous specific details, one of ordinary skill
in the art will recognize that the invention may be embodied in
other specific forms without departing from the spirit of the
invention. Thus, one of ordinary skill in the art would understand
that the invention is not to be limited by the foregoing
illustrative details, but rather is to be defined by the appended
claims. On the same note, the modulation formats of CDMA and OFDM
were used as examples. The data packets can be constructed
conforming to any wireless communication standard.
[0188] Those of skill in the art would understand that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0189] Those of skill would further appreciate that the various
illustrative logical blocks, modules, circuits, and algorithm steps
described in connection with the embodiments disclosed herein may
be implemented as electronic hardware, computer software, or
combinations of both. To illustrate this interchangeability of
hardware and software, various illustrative components, blocks,
modules, circuits, and steps have been described above generally in
terms of their functionality. Whether such functionality is
implemented as hardware or software depends upon the particular
application and design constraints imposed on the overall system.
Skilled artisans may implement the described functionality in
varying ways for each particular application, but such
implementation decisions should not be interpreted as causing a
departure from the scope of the present invention. Moreover, method
steps may be interchanged without departing from the scope of the
invention.
[0190] The various illustrative logical blocks, modules, and
circuits described in connection with the embodiments disclosed
herein may be implemented or performed with a general purpose
processor, a Digital Signal Processor (DSP), an Application
Specific Integrated Circuit (ASIC), a Field Programmable Gate Array
(FPGA) or other programmable logic device, discrete gate or
transistor logic, discrete hardware components, or any combination
thereof designed to perform the functions described herein. A
general purpose processor may be a microprocessor, but in the
alternative, the processor may be any conventional processor,
controller, microcontroller, or state machine. A processor also may
be implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core, or any other such configuration.
[0191] The steps of a method or algorithm described in connection
with the embodiments disclosed herein may be embodied directly in
hardware, in a software module executed by a processor, or in a
combination of the two. A software module may reside in RAM memory,
flash memory, ROM memory, EPROM memory, EEPROM memory, registers,
hard disk, a removable disk, a CD-ROM, or any other form of storage
medium known in the art. An exemplary storage medium is coupled to
the processor such the processor may be read information from, and
write information to, the storage medium. In the alternative, the
storage medium may be integral to the processor. The processor and
the storage medium may reside in an ASIC. The ASIC may reside in a
user terminal. In the alternative, the processor and the storage
medium may reside as discrete components in a user terminal.
[0192] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or utilize
the present invention. Various modifications to these embodiments
will be readily apparent to those skilled in the art, and the
generic principles defined herein may be applied to other
embodiments without departing from the spirit or scope of the
invention. Thus, the present invention is not intended to be
limited to the embodiments shown herein but is to be accorded the
widest scope consistent with the principles and novel features
disclosed herein.
[0193] The power allocation (.alpha..sub.i) to the various users
can be indicated in a variety of methods. One means is to partition
the range (0,1) into a number of smaller levels and indicate the
level which best approximates the power allocation. Another method
is to indicate the requested data rate (DRC) and the packet format
utilized to convey the data. The mobile will then calculate the
fraction of power allocated.
* * * * *